



Class TX_5.4£- 

Sook J\A_. 

CopyrightN 

COPYRIGHT DEPOSIT. 



The Engineers' Examiner 



For the aid of those who wish to obtain an 

engineer's license, and a guide for 

self-examination, including 

Exhaustive Instructions for Valve-Setting. 



By HENRY H. KELLEY. 

Originally Published in 
The Engineer. 



ILLUSTRATED. 



1903. 

THE ENGINEER PUBLISHING COMPANY, 
CLEVELAND. 



THE LIBRARY OF 
CONGRESS,. 

Two Copies' Received 

JUN 10 1903 

U Copyright Entry 

CUSS 0U xXc Nc 

(=> i o I i 
COPY B. 






Introductory Note* 



This work is not placed before the public as a complete 
examination, such as many of -the catechisms are represented 
to be, but rather to give the reader an idea of the scope of an 
examination and the principal subjects covered. It is proba- 
ble that the average examiner asks more questions, but the 
information necessary to pass a fair examination for a station- 
ary engineer's license is, we believe, contained in the answers, 
though in condensed form. 

The chapters on valve-setting will be found of great value 
to the man desiring to prepare for an examination. The 
requests for copies of The Engineer containing the articles 
were in so many instances accompanied by the statement 
that they were desired as an aid to the procurement of a 
lie erse tlat it was decided fo include the series in the volume. 
These are placed before the examination because we believe 
they will interest more readers. 

The Publishers, 



Copyrighted J903> by The Engineer Publishing Co. 



INDEX. 



Admission 9 

Apparatus, what requires most 

attention 113 

Atmospheric pressure 122 

Boiler, cleaning a 133 

different seams in 115 

drop-rlue 117 

evaporating power of a 128 

feeding a 132 

for steam in large quantities. 138 
for steam at high pressure.. . 138 

return-flue 114 

return tubular 114 

room, entering a strange 136 

scale, effect! on steam mak- 
ing 139 

removing and preventing. 139 

Scotch, marine 115 

thickness of, for given pres- 
sure 126 

tubes, why require cleaning. 137 

types of in common use 114 

vertical 116 

water tube 116 

what is a 115 

Bridgewall, distance from shell. 125 

Brown engine 99 

equalizing the cut-off U 7 

Chimney, capacity of 130 

draft in . 130 

what is a 130 

Clearance, volume of to find. 145-154 
what it is 144 

Coal burned per square foot of 
grate 130 

Compression 11-13 

in Corliss engine 98 

Condensation, cylinder table 
for. 152 



Condenser, what it is, why used. 154 

Corliss engine, valves 81 

Curve, hyperbolic, to draw 153 

Cut-off 9 

riding 3* 

riding, to set 38 

Dead-center 79 

Draft, natural and forced 130 

of cold air on boiler 133 

Eccentric-rod, adjusting the.... 21 

Energy, force and power 150 

Engine, advantages of com- 
pound 137 

direction of how determined. 144 
horse-power of, to find.. . 144-147 

lining up 148 

high and low speed 143 

placing on dead-center 148 

throttling and automatic cut- 
off 146 

what is an 143 

work of, how expressed 144 

Engineer, qualifications of 110 

studies for Ill 

Exhaust 10 

Expansion 10 

number of 146-148 

Feed water heater 140 

forcing water through 141 

Fire, banking a 131 

Force, what is a 150 

Governor, shaft 49 

Grate, a good furnace 130 

distance from shell 125 

surface 122-125-129 

Heat, latent 122 

Heating surface 122-123 

Horse-power, definition of 144 



Hyperbolic curve, to draw 153 

Indicator diagram 151 

what it indicates 150 

Injector, operation of 143 

what is an 115-142 

Lead, object of 14 

Link-motion, crossed eccentric- 
rods 73 

equalizing cut-off 67-79 

equalizing lead 65-77 

setting by marks 70 

slipoflink 75 

with rockershaft 58 

without rocker-shaft 76 

Latent heat 122 

Lap, object of 4 

Piston, engine 145 

Power, what it is 150 

Pressure, atmospheric 122 

Pressure, gauge 143 

adjusting pointer 148 

mean effective, initial, aver- 
age, terminal and back 160 

safe-working 117-126 

to obtain mean effective and 

terminal «... 136-151 

Pump, capacity of 140 

capacity, to determine 142 

data required 142 

what is a 115 

Pumping water against pressure 142 

effect of temperature on 14 i 

Rocker-shaft 26 

Safety-valve, connecting to 

boiler 126 

kinds of 120 

lever 119 

size required - 121 

weight, pressure, length of 
lever 121 



Seam, single and double riv- 
eted H7 

Smoke 131 

Steam gauge 126 

room in boiler . . 122 

Surface, grate 122 

heating 122 

Table of lap of Corliss valves.. . 98 
showing per cent of cylinder 

condensation 152 

Tensile strength 118 

Valves and their adjustment 3 

blow-off 135 

Corliss 81 

to set 88 

of Brown engine 99 

to reverse 108 

to set 104 

piston 41 

setting the 45 

plain D, operation and set- 
ting 14-21 

semi-rotary 28 

setting the 29 

Vacuum, to measure without 

gauge 1 22 

what it is 98 

Water, boiling point and effect 

of pressure on 12S 

cause of entering pump cyl- 
inder 141 

column, connecting up ... . 126 
feeding a boiler with cold ... 13* 

feed, saving by heating 136 

heated by exhaust steam 140 

level, dangerously low 138 

to ascertain the true 137 

line, where maintained 134 

supply interrupted 135 

weight of, from diagram 152 



Engine Valves and their Adjustment 



The Plain D Slide-Valve. 

Although the slide-valve is of very simple form, and one 
of the most familiar types of valve to the average engineer, 
there are many engineers who do not feel competent to under- 
take the job of setting it. One reason for this feeling of incom- 
petency lies in the fact that they do not understand the prac- 
tical working of a slide-valve on its seat— that is to say, they 
have not a clear idea of the proper position of valve, piston, 
crank and eccentric, at any part of the stroke, and unless an 
engineer can picture these positions and have them clearly 
defined in his mind, he is apt to find valve-setting very much 
of a puzzle: 

A consideration of the relative position of piston to valve 
at various points in the stroke will be taken up before enter- 
ing upon the work of setting valves. A clear understanding 
of the operation of the plain D slide-valve is very essential to 
a complete knowledge of other types. 

There are those who instead of studying the working of a 
valve and learning to set it by a thorough knowledge of its 
various functions, learn a rule for setting the various types of 
valves. 

In the latter case the information soon becomes unreliable 
and the degree of accuracy realized in setting a valve is there- 



4 THE PLAIN D SLIDE-VALVE. 

fore in proportion to the clearness with which they can recall 
the exact wording of the rule. It is hoped that the engineers 
who will read carefully the following explanations of the 
working of slide-valves and valve-gears will be able to set any 
valve without the aid of a rule. 

Fig. i represents a sectional view of a plain slide-valve and 
the steam and exhaust ports. The valve is represented as 




Fig. i. 

occupying a position known as " mid-travel" and when in this 
position it stands centrally over the ports. The position of 
mid-travel is also desirable when we wish to measure the out- 
side or steam lap, and the inside or exhaust lap of a valve. 

The distance between a and b, Fig. i, is called the outside 
or steam lap, and is the amount or distance that the outer 
edges of the valve extend beyond the outer edge of the steam 
ports when occupying the above position, and therefore con- 
stitutes the amount the valve lafs over the ports— hence the 
term " lap," 



THE PLAIN D SLIDE-VALVE. 5 

Lap is usually measured at one end 01 the valve only, so 
that a valve lapping over the steam port at each end to the 
amount of one-half inch, we say has one-half inch lap. The 
distance between c and d y Fig. i, is called the inside or ex- 
haust lap, and is the distance or amount that the edges of the 




Fig. 2. 



Fig. 3. 



cavity extend beyond or laf over the inner edges of the steam 
ports when the valve occupies the position of mid-travel, and 
is measured at one port only, as in the case of outside lap, 

>,The uses and advantages of outside and inside lap will be 
described later in connection with the operation of a valve. 
There are various means employed for attaching the valve 



6 THE PLAIN D SLIDE-VALVE. 

to the valve-stem, one of which is shown in Fig. 2, which con- 
sists of a band of iron called a " yoke," the inside of which is 
made to fit over the upper part of the valve, which has been 
prepared to receive it as shown in section in Fig. I. The 
valve-stem is screwed into the boss on the yoke and secured 
by a nut as shown. 

To move the valve on the stem, it is necessary to loosen 
the valve-stem in its connection with the eccentric-rod, and 
also the nut which secures it in the yoke, then turn the valve- 




Fig. 4. 

stem in the yoke until the desired movement has been ob- 
tained. Another method of connecting the valve to the valve- 
stem is shown in Fig. 3. This consists 'of an oblong nut of 
liberal dimensions, screwed on the valve-stem and fitted 
into the recess in the back of the valve as shown below it. 
The valve may be moved on the valve-stem by loosening the 
stem as described above and turning the rod in the nut until 
the required distance is obtained. A third method often 
employed is shown in Fig. 4, in which the opening o is cored 
or drilled out somewhat larger than the valve-stem, the latter 



THE PLAIN £> SLtDE-VALVE. f 

being slipped through the opening o and the valve screwed 
to the valve-stem by means of the jamb-nuts as shown. 

In the above methods, or in any other method which may 
be employed for attaching a valve to the valve-stem, the valve 
must be left free to move in a vertical direction, or at right 
angles to the valve-stem and with as little lost motion as pos- 
sible between the yoke, nut or jamb-nuts as the case may be. 




Fig. 5. 

The object sought in allowing a valve to thus freely move 
on the valve-stem is to avoid springing the stem, which would 
occur as the valve becomes worn after long use, or after hav- 
ing been scraped and refitted to its seat; and also in case 
there should be an accumulation of water in the cylinder, the 
water not being compressible, would be forced back through 
the port by the advancing piston, and were the valve to be 
rigidly secured to the valve-stem, the valve in being raised 



8 



THE PLAIN D SLIDE-VALVE 



from its seat by the water would badly spring if not break the 
stem. Having been sprung the stem would bind very hard 
in the stuffing-box and in a short time would not only put an 
end to the stem but would destroy the stuffing-box as well. 

We will now consider the manner in which a valve admits 
and exhausts steam to and from the cylinder. Fig. 5 repre- 
sents the position of the valve and piston at the commence- 




Fig. 6. 

ment of the stroke, also the corresponding position of the 
crank and eccentric. 

It will be noticed that the valve has already moved far 
enough to open the steam port a very little, thus admitting 
steam to the cylinder and filling the port and clearance space 
with steam at nearly initial pressure before the crank-pin 
leaves the dead-center. 

The valve has begun its active stroke before the piston 



THE PLAIN D SLIDE-VALVE. 9 

begins its stroke; in other words the valve is in the lead of 
the piston, therefore the amount that the valve opens the 
admission port while the crank is on the dead-center is called 
"lead." Now, as the piston begins to move in the direction 
of the arrow the valve also moves in the same direction and 
so continues until arriving at the position shown in Fig. 6, 
which represents the valve as having completed its stroke 





Fig. 7. 

and ready to commence its return stroke, also the relative, 
position of the piston in the cylinder and that of the crank 
and eccentric. The steam port is now wide open and the 
piston has moved to, approximately, one-quarter stroke, and 
when it has moved to the point or position indicated in Fig. 
7, the valve has then returned a sufficient distance to just 
close the steam port and produce what is known as " cut-off. T ' 
The point in the stroke reached by the piston at the moment 



to 



THE PLAIN D SLIDE-VALVE. 



cut-off takes place is called the "point of cut-off." In this 
case it is at about five-eighths stroke. It will be noticed now 
that the edge of the exhaust cavity in the valve (left-hand 
side in drawing), Fig. 8, is beginning to open the port to the 
exhaust and establishing communication between the space .9 
in the cylinder and the cavities in the valve and valve seat as 




^// ///////////// // / ///// // M/ 



Fig. 8. 



indicated by the arrow. The piston has moved from the posi- 
tion shown in Fig. 7 to that shown in Fig. 8 after cut-off took 
place or occurred; in other words the piston moved through 
the distance between the positions shown in Figs. 7-and 8 un- 
der the expansive force of steam alone, or under " expansion" 
as it is called. 

We then understand the term u expansion " to mean the 
distance the piston moves in the stroke after cut-off takes 



THE PLAIN D SLIDE-VALVE. tl 

place and up to the point where release or exhaust com- 
mences. Again referring to Fig. 8 we find that the right-hand 
edge of the exhaust cavity has just closed the opposite port 
through which steam from the opposite side (space V) of the 
piston has been exhausting, and as the piston has not yei 
reached the end of its stroke, all the steam contained in 
space s' in the cylinder has not been pushed out by the 
piston, a portion of this exhaust steam having been entrapped 
in the cylinder as represented by the arrow. 

That portion of the exhaust steam which has been thus 
shut in the cylinder is crowded or compressed into the 
clearance space when the piston completes its stroke. 

It requires some force to compress this amount of steam 
into so small a space, therefore the piston meets with re- 
sistance as soon as it commences to crowd this steam into 
the clearance and this resistance increases as the piston ad- 
vances and until it reaches the end of its stroke. Compres- 
sing a portion of the exhaust steam into the clearance as 
above described is called " compression," and the pressure of 
the steam thus compressed when the piston reaches the end 
of the stroke is called the pressure of compression; and that 
point in the stroke reached by the piston at the moment the 
exhaust port is closed is called the "point of exhaust closure" 
or the " point of compression." 

This completes one full stroke of the piston, the return 
stroke being made under precisely the same conditions. Let 
us consider for a moment the object in giving a valve " lead " 
which you will remember is the amount the valve opens the 
steam port while the crank is on the dead-center, as shown in 
Fig. 5. The object sought in giving a valve lead is, primarily, 



12 THE PLAIN D SLIDE-VALVE. 

to cushion the piston at the end of the stroke, thereby 
effecting an easy reversal of the motion or movement of the 
reciprocating parts of the engine. 

When the piston has advanced to within a short distance 
of the end of the stroke the valve opens the port a little and 
admits steam to the cylinder, the pressure rising rapidly and 
almost to boiler pressure, which has a tendency to stop the 
piston. The latter in turn imparts this tendency to stop to the 
crosshead and connecting-rod, thus relieving the crank-pin 
of much of the strain in bringing these parts to a complete 
stop at the end of the stroke and again starting them in the 
opposite direction. Again in giving a valve lead the port is 
opened wide earlier in the stroke of the piston, and at a point 
where the connecting-rod and crank occupy a position in 
which the greatest force is obtained in turning the crank- 
shaft. 

Lead also produces in an engine that quality known 
among engineers as being " smart," that is, being quick in 
responding to the action of the valve and especially when 
starting. The cause of this quality of " smartness " is that 
when a valve is given lead the port and clearance space are 
filled with steam at high-pressure before the piston begins its 
return stroke, therefore there is no waiting for pressure to 
accumulate behind the piston when the crank-pin moves 
away from the dead-center. 

The object sought in producing compression in an engine 
cylinder is quite similar to that in giving a valve lead, 
namely, to arrest the momentum of the reciprocating parts 
of the engine, or the piston, rod, cross-head and connecting- " 



THE PLAIN D SLIDE-VALVE. 13 

rod at the end of the stroke, thus lessening the strain upon 
the crank-pin as explained above. 

But the effect of compression and the method of obtaining 
the cushioning effect are different from those in the case of 
lead and therefore "cushion" (lead) and "compression" should 
not be considered as one and the same thing. The cushion- 
ing effect of compression is obtained by shutting in a portion 
of the exhaust steam instead of admitting live steam from 
the boiler. 

At the instant the exhaust valve closes there is no pressure 
in the cylinder (on the exhaust side of the piston) except 
that due to the exhaust steam or exhaust pressure. 

But, as the piston advances and begins to crowd the steam 
thus shut in the cylinder into the clearance space, pressure is 
gradually produced, reaching the maximum when the piston 
has completed its stroke. 

From this it will be understood that, as the pressure grad- 
ually increases as the piston advances toward the end of its 
stroke the cushioning effect must also be gradual, thus bring- 
ing the rapidly moving parts of the engine gradually to rest 
at the end of the stroke without a jar or pound. The pressure 
of compression is very rarely as high as that obtained in the 
case of lead, for, to increase the pressure of compression up 
to the initial pressure would require that a greater amount or , 
volume of steam be shut in the cylinder by closing the ex- 
haust port, and in order to do this the exhaust valve would 
have to close the port very early in the stroke, and the power 
absorbed in compressing the larger volume of steam to 
initial pressure would materially lessen the useful work of 
the engine. 



H 



THE PLAIN D SLIDE-VALVE. 



Ill giving a valve lead in an engine in which the piston is 
partially cushioned by compression we have but to make up 
the difference in pressure between that of compression and 
the initial pressure, hence the lead in this case may be re- 
duced, thus often effecting a saving in steam. 

Objects of Outside and Inside Lap. 

Fig. 9 represents the position of the valve, piston, crank 




Fig. 9. 

and eccentric at the commencement of the stroke, which is 
to be in the direction indicated by the arrow. The valve in 
this case has no lap, that is, the outer edges of the valve do not 
extend beyond the outer edges of the steam ports, nor do the 
edges of the exhaust cavity in the valve extend beyond the 
inner edges of the steam ports when the valve occupies the 
position of mid-travel. Again referring to Fig. 9 we find the 
valve has opened the admission port a very little, or to the 



THE PLAIN D SLIDE-VALVE. 



IS. 



amount of the " lead," and the center line of the eccentric 
stands at right angles (or nearly so) to the center line of the 
crank. Now, as the piston moves in the direction indicated 
by the arrow,, the eccentric, and therefore the valve, also 
.moves in the same direction, and so continues to move until 
arriving at the position shown in Fig. 10. The admission port 
is now wide open and the eccentric has reached the dead- 
center farthest from the cylinder, and is therefore ready to 





Fig. 10. 

commence its return stroke, while the piston has only moved 
to about one-half stroke. 

Fig. ii shows the piston as having completed its stroke, 
the valve having just closed the admission port and effected 
the "cut-off." It will be seen from this that the steam has 
followed the piston throughout the entire stroke before the 
cut-off occurred, allowing of no expansion whatever. 

The exhaust port is opened at the same instant that the 
cut-off takes place, exhausting steam at initial pressure into 



16 



THE PLAIN D SLIDE-VALVE. 



the atmosphere, no work having been done in the cylinder by 
expansion — which would result in an enormous waste of 
steam, for economy in the amount of steam taken from the 
boiler can only be realized by admitting a certain quantity 
of steam to the cylinder and allowing it to expand, thug 
getting out of it all the good (expansive force) there is in it. 

An engine having a valve with no steam lap cannot 
be run at high speed without entailing an additional loss 




Fig. ii. 

(this time in power) due to excessive compression, for the 
exhaust cavity in the valve cannot be widened beyond 
that shown in Fig. II, which would allow the exhaust port 
to be opened before the piston reached the end of its 
stroke, allowing a free exhaust to be realized; for, to widen 
the exhaust cavity would reduce the thickness of the valve 
at A, Fig. 12, and permit live steam to pass from the steam- 
chest to the exhaust pipe as the valve passed over the 
port as shown. The drawing in Fig. 5 represents a valve 



THE PLAIN D SLIDE-VALVE. 17 

having lap. The engine is in the same position as in Fig. 9 
and the valve also has opened the steam-port to the amount 
of the lead. So far both cases are identical, but turning to 
the eccentric we find a change, and instead of its central line 
standing at right angles to the crank, we find it inclined away 
from a vertical position. This position is due to the fact that 
the valve has lap, for if the eccentric in Fig. 5 were to be 
set in the position shown in Fig. 9. the piston would have to 
move to about one-half stroke before the valve would open 



47, 




/IT- 



Fig, 12. 

the port; therefore, as this would be impracticable, the ec- 
centric must be moved around on the shaft and until it has 
moved a certain distance beyond the position shown in Fig. 
9, which distance is determined by the amount of lap on the 
valve, and also the amount of lead, for the eccentric must 
be moved away from a vertical position in order to draw the 
valve away from its position of mid-travel, and far enough to 
open the steam port to the amount of the lead. 

Many engineers maintain the mistaken idea that there is 
a particular angle at which an eccentric should be set with 
reference to the center line of the crank, but upon studying 



l8 THE PLAIN D SLIDE-VALVE. 

the foregoing figures it will be plainly seen by most engineers 
that the angle referred to will and does change with different 
amounts of lap and lead, and this change may be effected 
any number of times in almost any engine withou* seriously 
impairing its running qualities. 

Fig. 6 shows the position of the piston in the cylinder 
when the port is wide open and the eccentric has now reached 
its dead-center. By comparing the position of the piston 
shown in Figs. 6 and 10 it will be seen that the piston has 
not moved as far in the stroke when the eccentric reaches its 
dead-center and when the valve has lap as in the former 
case. 

Fig. 7 shows the valve as having completed its stroke in 
the direction of the arrow, and returned sufficiently to close 
the admission port, producing "cut-off," which, in this case 
is at about two-thirds stroke instead of full stroke as in the 
case of no lap. 

Fig. 8 represents the piston as having advanced a little 
further in the stroke, and after cut-off has occurred or under 
expansion. The valve is now beginning to open the exhaust 
port, although the piston has not yet reached the end of its 
stroke, thus allowing a free exhaust, for by the time the 
piston reaches the end of the stroke, the valve will have 
opened the port to the exhaust to nearly one-half the width 
of the port, while in Fig. ii, the valve was just beginning to 
open the port to the exhaust when the piston had completed 
its stroke. 

From the foregoing we learn that the object in having lap 
on a valve is to cause the cut-off to occur earlier in the stroke, 
or before the piston has completed its stroke, and the advan- 



THE PLAIN D SLIDE-VALVE. I9 

tage to be gained is in allowing the piston to move a certain 
distance after the supply of steam has been shut off, or under 
expansion; that is, in shutting off the steam from the cylinder 
before the piston reaches the end of the stroke, the whole 
cylinder is not filled with steam from the boiler, but only that 
portion of the cylinder measured from the commencement of 
the stroke to the point of cut-off, the remainder of the stroke 
of the piston being accomplished by the expansive force of 
the steam only. The object in having inside or exhaust lap 
on a valve (which is rarely to be found in fast running en- 
gines) may be understood by referring to Fig. 8. If the width 
of the exhaust cavity in the valve had been lessened the port 
would not have been opened to the exhaust until the piston 
had moved nearly to the end of its stroke. 

This would have caused the steam to follow the piston 
further in the stroke which, under certain conditions, might 
prove to be an advantage, but we also see that if the width of 
the cavity had been reduced it would have caused the ex- 
haust port (Fig. 8) to be closed earlier in the stroke, thereby 
shutting in a larger volume of steam which would have been 
compressed to a higher pressure than would be desirable in a 
fast-running engine. 

The object of inside lap on a valve then, is to cause the 
opening of the port to the exhaust to occur later in the stroke 
and the closing of the exhaust port to occur earlier in the 
return stroke. 

To return for a moment to the advantages gained in hav- 
ing steam lap on a valve: 

Many engineers who are without means of obtaining the 
mean effective pressure, or even the average pressure in an 



20 THE PLAIN D SLIDE-VALVE. 

engine cylinder, still persist in taking the boiler or initial 
pressure as the mean effective pressure when computing the 
horse power of an engine. 

From the foregoing it will be see*n that this method is 
entirely wrong except in engines having valves with no lap 
and which, happily, are "few and far between" nowadays. 
The above method can only be of service and reliable when 
steam is admitted during the full stroke of the piston, for in 
this case the mean effective pressure becomes the initial 
pressure minus the back pressure and the horse power de- 
veloped would largely exceed that of an engine having a 
valve provided with lap, the size of the cylinder, speed and 
initial pressure being the same. To illustrate this point let 
us assume an engine taking steam full stroke and one in 
which the cut-off occurs at one-half stroke and note the differ- 
ence in horse power developed. Diameter of cylinder (in 
both cases) =ten inches; length of stroke = 18 inches and 
running at 150 revolutions per minute. Initial pressure = 
80 pounds per square inch and back pressure in first case 
= eight pounds and in second case three pounds (gauge). 

The horse power with no lap would be: 

PLAN 78.54 X 3 X 72 X 150 

= = 77.11 horse power. 

33,000 33> 000 

In this formula P = area of the piston, L = length of 
stroke, A == mean effective pressure and N = number of 
strokes per minute. 

The horse power when cutting off atone-half stroke would 
be: 



THE PLAIN D SLIDE-VALVE. 21 

PLAN 78.54 X 3 X 53-2 X 150 



= 56.97 horse power. 



33,000 33,000 

The foregoing examples plainly indicate that an engineer 
who uses by-gone methods in computing the horse power of 
an engine makes a serious mistake and one which should be 
looked upon as inexcusable in these days when engineering 
literature may be had almost for the mere asking. 

The above illustration also indicates that an engine having 
a valve provided with steam or outside lap, requires a -larger 
cylinder than one in which the valve has no lap, in order to 
develop a given horse power with a given initial pressure — 
other things being equal. While the larger cylinder would 
be more costly at the outstart, yet the saving in steam effected 
by the lap and in turn an earlier cut-off, as previously ex- 
plained, would in a comparatively short time pay for the 
increase in the first cost, and after the amount saved had 
equaled the extra expense of the larger cylinder, the saving 
would be " clear gain" as long as the engine continued to run. 

Adjustment of the Eccentric-Rod and Setting the Valve, 

We will now take up the adjustment of the eccentric-rod 
and method of setting a slide-valve. It may be well to say 
here, that no valve operated by means of an eccentric and 
eccentric-rod can be set in a satisfactory manner until the 
eccentric-rod has been adjusted to the proper length. 

This may be understood by referring to Fig. 13 which rep- 
resents the eccentric of an engine placed on its dead-center 
nearest the cylinder. It will be noticed that the valve has 
not fully opened the steam port nearest the crank. This is 



22 



THE PLAIN D SLIDE-VALVE. 




THE PLAIN D SLIDE-VALVE. 23 

caused by the eccentric-rod being too short and therefore the 
eccentric is unable to move the valve far enough to give full 
port opening. 

Now, if the eccentric were to be turned to the opposite 
dead center or the center farthest from the cylinder we 
should find that the valve would have moved too far. or, in 
other words, had moved more than enough to open the port 
wide. The whole movement or travel of the valve would be 
one-sided, and in the direction of the eccentric, and as this 
one-sided action is due to the eccentric-rod being too short 
the remedy lies in lengthening the rod. To do this we first 
place the eccentric in the position shown in Fig. 13, then pro- 
ceed to lengthen the rod until the valve has moved to the 
position shown in Fig. 14, which represents the proper position 
of the valve when the eccentric occupies the position as 
shown, viz., having just opened the port wide. If however, 
when turning the eccentric to the position as shown in Fig. 13, 
we had found that the valve^had more than opened the port, 
the eccentric-rod would then have been too long and the 
remedy would have been to shorten the rod until the position 
shown in Fig. 14 was obtained. 

After having adjusted the eccentric-rod to the proper 
length we are ready to set the valve and we will assume the 
engine is to run "over," that is, if we were to stand at the 
opposite end of the engine from the crank, and facing the 
crank, should see the crank-pin rise as the piston moved away 
from the end of the cylinder at which we were standing the 
enjine would then be running " over." When learning to set 
the valves in any engine, and in fact, in all engines, it is a 
good phm to have a common starting point, that is, no matter 



24 



THE PLAIN D SLIDE-VALVE. 



what type of engine and valves are about to be set, always 
place the eccentric and crank on the same dead-center, and 
preferably the dead-center nearest the cylinder. 

The advantage to be gained in having a common starting 
point and especially when learning to set valves, is that after 
the direction in which the engine is to run and the type of 
valve-gear employed are obtained all that is required is to 





Fig. 15. 

remember what direction of eccentric corresponds to the 
given type of valve-gear. 

Fig. 15 represents the position of the valve, piston, crank 
and eccentric at the commencement of the stroke, which is to 
be in the direction indicated by the arrows. 

Now, as the piston begins to move, more steam must be 
admitted to the cylinder, and by referring to the drawing it 
will be seen that in order to accomplish this the valve and 
the eccentric must move in the same direction as the piston; 
therefore in setting a slide-valve with plain gear we must 



THE PLAIN D SLIDE-VALVE. 



25 



move the eccentric on the shaft (from the dead-center) in 
the direction in zvhich the engine is to ru?i until the valve 
opens the admission port to the amount of the lead which 
position is shown in Fig. 15. Never mind the position of the 
eccentric relative to the crank — that will take care of itself. 
All that is to be considered is the direction in which to move 
the eccentric and the position of the valve over the ports.. 
The set screws are now to be tightened, thus securing the 





Figs. 16 and 17. 

eccentric to the shaft. We do not knozv as yet whether the 
valve will open the opposite port to exactly the same amount 
as first obtained, therefore the engine is to be turned around 
to the opposite dead-center from that shown in Fig. 15 and the 
amount of lead determined. 

Should a difference be found in the amount of lead from 
that first obtained, move the valve on the valve-stem to the 
amount of one-half the difference in the lead at either dead- 



26 THE PLAIN D SLIDE-VALVE. 

center, and which may be done by adjusting the jamb-nuts, 
nut or yoke as explained in a previous chapter. 

It is better under ordinary circumstances to move the 
valve on the valve-stem or adjust the length of the stem for 
the purpose of equalizing the lead, than to change the length 
of the eccentric-rod after it has been properly adjusted. 
Having equalized the lead as described, the valve will be 
properly set. 

The foregoing method of setting a slide-valve applies to 
engines equipped with a simple valve-gear; that is, without 




Fig. 19. 

a rocker-shaft or other reversing mechanism placed between 
the eccentric and valve. It will be well to mention here that 
there is one form of rocker-shaft which will not change the 
foregoing method of setting a valve, and which is shown in 
Fig. 16. In this type of rocker-shaft the valve and eccentric 
both move in the same direction at the same time, so that as 
far as the influence of the rocker-shaft upon the movement 
of the valve is concerned it is equivalent to having the ec- 
centric-rod connected directly with the valve-stem, hence no 
change is to be made in the foregoing method of setting a 






TFE PLAIN D SLIDE-VALVE. 2J 

valve when this type of rocker-shaft is employed. We will 
now consider a method of setting a slide-valve when a 
rocker-shaft as shown in Fig. 17 is employed, and which re- 
verses the movement of the valve relative to that of the 
eccentric. 

Referring to the drawing it will be seen that when the 
eccentric-rod moves in the direction of the arrow the valve 
moves in the opposite direction, which is also indicated by an 
arrow. This type of rocker-shaft forms what is known as a 
lever of the first class, viz., power is applied at one end 
(lower end), fulcrum in the middle and the weight, or re- 
sistance, at the other end (upper end). Before attempting to 
set the valve the eccentric-rod must be adjusted to proper 
length and in precisely the same manner as described in the 
case of a plain or simple valve-gear. The only change to be 
noticed is in the opening of the ports, for as the rocker-shaft 
reverses the direction of the valve relative to that taken by 
the eccentric-rod, the opposite port to that shown in Fig. 14 
will be open when the eccentric occupies the position shown 
in the same figure. Bearing in mind the fact that the ec- 
centric must move in the o^fosite direction to that in which 
the valve moves, we see by referring to Fig. 18 that as the 
piston begins to move in the direction of the arrow the valve 
must also move in the same direction, and that the eccentric 
must move in the offiosite direction, and in order to do this it 
would have to be located somewhere in the vicinity of o, 
therefore, to find the exact location we turn the eccentric on 
the shaft in the ofjiosite direction to that in which the engine 
is to run until the valve opens the port to the amount of the 
lead as shown in Fig. 18. 



28 THE SEMI-ROTARY VALVE. 

By again referring to the drawing it will be seen that when 
the eccentric moves toward the cylinder the valve moves 
toward the crank, or, in the direction in which the engine is 
10 run, and thus corresponds to the movement of the valve 
as explained in the previous case, therefore the valve is set 
as far as the eccentric is concerned; all that remains is to 
equalize the lead, which is accomplished by turning the 
engine first to one dead-center and then the other, and 
measuring the amount of port opening or lead, which should 
be divided equally between the two ports by moving the 
valve on the stem, or, adjusting the length of the valve-stem 
as explained in the case of the simple valve-gear. 

The Semi-Rotary or Rocker Valve* 

The next to receive consideration is the semi-rotary or 
"rocker" valve so-called by some engineers, and which in 
reality is a plain "D "-valve working on a semi-circular 
valve-seat. The usual method of attaching semi-rotary valves 
to the valve-stem is shown in Fig. 19. The stem in this case 
extends at right angles to the direction in which the valve 
moves, the motion being imparted to the valve by means 
of the crank-arm A, attached to the outer end of the stem, and 
which in turn receives motion from the eccentric by means 
of the eccentric-rod. The oblong block B, is secured to the 
inner end of the valve-stem and fitted into the recess in the 
back of the valve, as shown immediately below it. This con- 
struction permits the valve to move in a vertical direction 
without springing the valve-stem the necessity for which was 
explained in connection with the plain slide-valve. The 
operation of a semi-rotary valve having the crank-arm A, in 



THE SEMI-ROTARY VALVE. 



2Q 




Fig. 20. 




Fig. 21. 



3° 



THE SEMI-ROTARY VALVE. 



the position shown in Fig. 19 is identical with that oi a slide- 
valve having a simple valve-gear, therefore further descrip- 
tion will be unnecessary. Some engines are built with the 
valve placed below the cylinder and the arm A placed in the 
opposite position to that shown in Fig. 19. This arrangement 
changes the movement of the valve relative to that of the 




Fig. 22. 

eccentric, having the same effect as the rock-shaft of the type 
shown in Fig. 17. 

The operation of a semi-rotary valve fitted with the crank- 
arm in the position shown in Fig. 19 (dotted lines may be 
understood by referring to Fig. 20 which represents the cyl- 
inder inverted) shows the position of the valve, crank-arm, 
crank and eccentric at the commencement of the stroke 
which is to be in the direction of the arrow. 

It will be noticed that the valve has opened tne admission 



THE SEMI-ROTARY VALVE. 



31 



pet to the amount of the lead, and the center line of the 
eccentric is inclined away from a vertical position, which is 
due to the fact that the valve has lap, also that when the 
eccentric-rod moves in the direction indicated by the arrow 
the valve moves in the opposite direction. 

Fig. 21 shows the position of the various members when 
the valve has completed its stroke and is ready to commence 




Fig. 23. 

its return stroke, the piston having moved to about one-fourth 
stroke. Fig. 22 represents the valve as having returned on 
the backward stroke sufficiently to close the admission port 
and effect the "cut-off." 

The difference between the positions shown in Figs. 22 and 
23 represents the distance the piston has moved after cut-off 
nas taken place or under expansion. 

The left-hand edge of the exhaust cavity in the valve has 



32 THE RIDING CUT-OFF. 

just commenced to open communication between the space S 
in the cylinder and the exhaust pipe, as indicated by the 
arrow, and, at the same time, the right-hand edge of the ex- 
exhaust cavity has just closed the port through which steam 
from the space S l , in the cylinder has been exhausting, thus 
entrapping a portion of the exhaust steam in the cylinder, as 
indicated by the arrow; therefore the steam which has been 
thus shut in the cylinder is compressed by the piston into the 
clearance space during the remainder of "the stroke. 

The similarity in the action of a semi-rotary valve to a 
slide-valve may be readily comprehended by comparing the 
drawings in both cases, viz., those representing the positions 
of valve, piston, crank and eccentric in the case of the semi- 
rotary valve and those representing the same members in 
connection with the slide-valve. The method of setting a 
semi-rotary valve with the crank-arm in the position shown 
in Fig. 19 (dotted lines) is precisely the same as in the case of 
a plain slide-valve having a rocker-shaft placed between the 
eccentric and valve, of the type shown in Fig. 17. 

The Riding Cut-Oft 

The anangement of valves in what is known among engi- 
neers as the " riding cut-off," comprises a ported main valve 
which lies next the cylinder (see Fig. 24) and an upper valve 
called the cut-off valve. The duty of the main valve is to 
admit steam to the cylinder, exhaust the same from the cyl- 
inder and produce compression. The duty of the cut-off 
valve is to shut off the supply of steam to the cylinder at the 
proper point in the stroke of the piston by closing the ports 
in the main valve. The back of the main valve forms the 



THE RIDING CUT-OFF. 



33 



valve seat for the cut-off valve, therefore the latter slides (or 
rides) on the upper side or back of the main valve, hence the 
term " riding cut-off.'* 

In order to save confusion which might arise in attempt- 
ing to carry the operations of both valves in mind at the same 
time we will consider them separately beginning with the 
main valve. 




Fig. 24. 



Fig. 24 represents the position of the main valve, piston, 
crank and main eccentric at the commencement of the stroke 
which is to be in the direction indicated by the arrow. The 
crank is now on the dead-center and the main valve has 
opened the admission port to the amount of the lead, the ex* 
haust port at the opposite end of the cylinder being open to 
about one-fourth the width of the port. This is called exhaust 
lead, the object and advantages of which were described in a 
previous chapter, Fig. 25 shows the position pf the piston, 



34 



THE RIDING CUT-OFF. 



crank and eccentric when the admission port is wide open, 
which occurs at about one-third stroke. 

The main eccentric has now reached the dead-center far- 
thest from the cylinder and the main valve has therefore com- 
pleted its outward stroke and is ready to commence its return 
stroke, as indicated by the arrow. 

Fig. .26 represents the position of the piston, crank and 




Fig. 25. 

eccentric when the main valve has returned on its backward 
stroke a sufficient distance to just close the admission port 
producing " cut -off" which is at about three-fourths stroke. 
Fig. 27 represents the piston as having moved a little farther 
in the stroke and after cut-off occurred, or under expansion. 
The main valve has now just closed the exhaust port (at the 
right in Fig. 27), thereby producing compression. We also 
notice that the admission port is now open a very little, estab- 
lishing communication between the space S in the cylinder 



THE RIDING CUT-OFF. 



35 



and the exhaust-pipe, or has opened the port to the amount 
of the exhaust lead (nearly). 

The difference in the position of the piston in Figs. 26 and 
27 indicates the distance the piston has moved under expan- 
sion, under the influence of the main valve only. From the 
foregoing it will be seen that the operation of a main valve in 
a riding cut-off is identical to that of a plain D valve having 
but little lap. The similarity may be made still more appar- 




FiG. 26. 

ent if the reader will compare the foregoing with the opera- 
tion of a plain slide-valve with little lap as previously de- 
scribed. 

We will now consider the effects produced by the addition 
of the riding cut-off valve. Fig. 24 represents as before the 
position of the piston, valves, crank and eccentrics at the com- 
mencement of the stroke. When the main valve occupies 
the position shown in Fig. 24 the cut-off valve has completed 
its outward stroke and has returned on its backward stroke to 



36 THE RIDING CUT-OFF. 

the position shown. This may be more fully understood by 
referring to the position of the cut-off eccentric. 

Fig. 25 shows the position of the cut-off valve when the 
main valve has opened the admission port in the cylinder to 
the fullest extent, and just about to close the port in the main 
valve and produce "cut-off/* which now occurs at about one- 
third stroke instead of three-fourths stroke as when under 
the influence of the main valve only. 




Fig. 27. 

Now, by comparing Figs. 26 and 27, we may readily 
obtain the distance the piston moved under expansion when 
under the influence of the main valve only, and by comparing 
Figs. 25 and 27 we may obtain the distance (nearly) the piston 
moved under expansion when the cut-off was effected by 
means of the cut-off valve, and we see too that the earlier 
cut-off has been obtained without changing the main valve in 
any particular. Therefore while the point of cut-off has been 
changed from three-fourths stroke to one-third stroke, the 



THE RIDING CUT-OFF. 37 

point of exhaust opening and the width to which e*xhaust-port 
has been opened and the point of compression all remain the 
same, and will remain the same for all points of cut-off unless 
the main eccentric is shifted on the shaft. In throttling 
engines the point of cut-off is changed (while the engine is 
running) by means of a hand-wheel or lever, placed at the 
end of the steam-chest farthest from the crank. By turning 
the hand-wheel in one direction the cut-off valve is lengthened 
and an earlier cut-off is the result, and turning the hand-wheel 
in the opposite direction, shortens the cut-off valve, producing 
a later cut-off. 

This arrangement is called an adjustable cut-off and in 
this case both eccentrics are fixed to the engine shaft — the 
speed of the engine being regulated by the governor, which, 
as the name of the engine implies, throttles the steam and 
maintains a uniform rate of speed by varying the pressure of 
steam admitted to the steam-chest, to suit the load on the 
engine, the point of cut-off remaining as set by the hand-wheel 
or lever at the end of the steam-chest. 

In the automatic cut-off engines the point of cut-off is 
automatically changed by the governor which is usually of 
the shaft type and which causes the cut-off eccentric to turn 
slightly on and around the shaft, advancing the position of 
the eccentric as the governor weights move outward, which 
in turn causes an earlier cut-off to take place, and again 
diminishing the advance of the eccentric as the speed of the 
engine decreases and the weights move toward the shaft. 
This in turn causes the cut-off to occur later in the stroke of 
the piston. This may be more fully understood by referring 
to Fig. 25. If the cut-off eccentric had been advanced to the 



38 THE RIDING CUT-OFF. 

position represented by the dotted line, it would have reached 
the dead-center (now occupied by the main eccentric) earlier 
in the stroke of the piston, and consequently would have 
returned far enough on its backward stroke to close the 
admission port in the main valve when the piston occupied 
the position shown in Fig. 25. 

On the other hand, if the governor had caused the cut-off 
eccentric to occupy a position corresponding to that of the 
main eccentric, the cut-off would have occurred when the 
piston had reached the position shown in Fig. 26. From this 
we see that, as the position of the cut-off eccentric is ad- 
vanced relative to that of the crank, the cut-off occurs earlier 
in the stroke of the piston, and as the advance of the cut-off 
eccentric is diminished, the cut-off occurs later in the stroke. 
The principal advantages to be derived from the use of the 
riding cut-off over a single slide-valve are that it permits the 
point of cut-off to be changed, either by hand or automatically 
as the case may be without altering first, the amount of lead; 
second, the point of exhaust opening and the length of time 
the exhaust port is open; third, the point of exhaust closure, 
or the point of compression. 

In slow and medium-speed engines it is an advantage to 
have the above operations occur at the same point in the 
stroke regardless of the point of cut-off, which cannot be ac- 
complished with a single valve in an automatic cut-off engine 
as will soon be explained. We will now consider a method 
of setting a riding cut-off. 

In setting the valves of a riding cut-off the main eccentric- 
rod must first receive attention and be adjusted to the proper 
length, which is done in precisely the same manner as in the 



THE RIDING CUT-OFF. 30 

case of a plain slide-valve which has been fully explained in a 
previous chapter. It should have been stated that the cut-off 
valve is to be removed before attempting to adjust the length 
of the main eccentric-rod, otherwise the cut-off valve (in some 
types of gears) might obstruct the view of the main valve. 
After having adjusted the main eccentric-rod to the proper 
length, place the crank on the dead-center nearest the 
cylinder and also turn the full side of the main eccentric to 
a corresponding position. Next, determine the direction in 
which the engine is to run, then turn the eccentric on the 
shaft in the same direction, and until the port in the main 
valve opens the admission port in the cylinder to the amount 
of the lead. Now, if the engine is to run over and the eccen- 
tric has been properly set, the main valve will occupy the 
position shown in Fig. 24. Fix the eccentric to the shaft and 
turn the engine to the opposite dead-center, when the amount 
of lead should be the same as in the first position. If not, 
equalize in the same manner as for a plain slide-valve. Now 
place the cut-off valve on the back of the main valve and 
connect to the valve-stem. The length of the cut-off eccen- 
tric-rod must now be adjusted to the proper length, but before 
doing so, place the main valve (by turning the engine) in its 
position of mid-travel. 

Turn the cut-off eccentric to the dead-center (either cen- 
ter) and measure the distance that the outer edge of the 
cut-off valve has moved beyond the inner edge of the port 
through the main valve, then turn the eccentric to the 
opposite center and again measure the distance as before. 
The distance referred to above must be equal when the 
eccentric occupies the above positions, viz., the dead-center. 



40 THE RIDING CUT-OFF. 

In other words, the outer edges of the cut-off valve must 
move equal distances beyond the ports in the main valve, 
when the cut-off eccentric is placed on its dead-center. For 
the sake of simplicity we will assume that the engine has an 
adjustable cut-off and we wish the same to occur at one-half 
stroke. Place the crank on the dead-center nearest the 
cylinder and the full side of the cut-off eccentric the same. 
Now turn the engine in the direction in which it is to run, 
until the crosshead reaches exactly one-half stroke. Now 
turn the cut-off eccentric in the same direction until the 
cut-off valve opens the port in the main valve and again just 
closes it, but no more. Fix the eccentric to the shaft and 
turn the crank over the center and until the crosshead again 
reaches one-half stroke (this time on the return stroke) when 
the cut-off valve should have just closed the opposite port in 
the main valve. If it does, then the cut-off will occur at 
one-half stroke during the forward and backward stroke of 
the piston, but should there be a difference, then the cut-off 
eccentric must be moved slightly on the shaft until the cut-off 
is equalized; that is, until it occurs at the same point in both 
the forward and backward strokes. This done, the valves 
will be properly set for one-half cut-off. 

It must be remembered by those not thoroughly familiar 
with the operation and setting of valves, it often happens 
that a valve will be badly "out," as engineers call it, when an 
engine is started up, after having the valve set as accurately 
as known methods will permit. The cause of this lies in the 
expansion of the cylinder, valve, valve-stem, etc., due to the 
heat of the steam, and should the valve be "out" sufficiently 
to cause the engine to run badly, the surest method of ascer- 



THE PISTON-VALVE. 



41 



taining the cause of the difficulty is in applying an indicator, 
which will show at a glance what expansion has done toward 
spoiling your work. 

The Piston- Valve. 

The piston-valve differs from the types of valves pre- 
viously illustrated, and, when properly made and fitted to 
the valve-chest, it represents a cheap and durable form of 




Fig. 28. 




balanced valve. As will be seen by referring to Fig. 29 
the piston-valve derives its name from its construction or 
form, being composed of two pistons P and P' connected 
together by the trunk T. The similarity that the piston-valve 
bears to the slide-valve in their relation to the steam-ports is 
shown in Figs. 28 and 29 which represent the two valves 
placed face to face, and also as having opened the steam- 
port to the amount of the " lead." In one type of piston- 
valve the trunk is made solid and when so made, steam is 
usually admitted to the cylinder at the ends of the valve as 
shown in Fig. 28. When this type of valve is employed the 



42 



THE PISTON-VALVE. 



operation of and the method of setting the valve are pre- 
cisely the same as in the case of the plain slide-valve, there- 
fore further description of this type of valve will be unneces- 
sary. Another type of piston-valve, shown in Fig. 30, is the 
one most commonly employed. In this type the trunk is cast 




Fig. 30. 

hollow, as shown, the valve-stem being screwed into the valve 
as indicated in Fig. 30. 

In this valve the steam is admitted to the cylinder on the 
inside or between the pistons of the valve, the exhaust from 
one end of the cylinder passes through the hollow trunk to 
the exhaust-pipe and the exhaust from the opposite end of 
the cylinder passes directly to the exhaust-pipe, as shown by 



THE PISTON-VALVE. 



43 



the arrows. This construction of valve permits exhaust steam 
only (and therefore steam of low pressure), to come in contact 
with and be held in by the joints between the valve-chest and 
the heads and also by the stuffing-box where the valve-stem 
enters the chest. 

The operation of a piston-valve may be understood by 
referring to Fig. 31 which represents the position of the valve, 
piston, crank and eccentric at the commencement of the 




Fig. 31. 



stroke which is to be in the direction of the arrow. The 
crank is now on the dead-center and the valve has opened 
the admission port to the amount of the lead. The opposite 
port is partly open to the exhaust, which opening you will 
remember, measures the amount of exhaust lead. Now, by 
referring to the crank and eccentric, it will be seen that as 
the former moves away from the dead-center in the direction 
of the arrow, the eccentric and therefore the valve, will move 
in the opposite direction, opening the port and so continuing 



44 



THE PISTON-VALVE. 



until arriving at the position shown in Fig. 32, which repre- 
sents the port as wide open. The eccentric has now reached 
its dead-center nearest the cylinder and is therefore, ready to 
commence its return stroke and cause the valve to close the 
port — while the piston has moved to about one-third stroke. 
The cause of the valve moving in the opposite direction to 
that of the crank is that the valve admits steam from the 
inside instead of the outside as in the case of the plain slide- 




FlG. 32. 

valve, (see Fig. 35) therefore, as the admission of steam takes 
place at the opposite end of the valve, so to speak, to that in 
the slide-valve, it is evident that the direction of the travel of 
the valve must also be in the opposite direction to that of the 
slide-valve when performing this function, if the engine is to 
run in the same direction in both cases. 

Fig. 33 represents the position of the piston, crank and 
eccentric at the point of cut-off which is at about two-thirds 
stroke. The valve has completed its stroke in the direction 
indicated in Fig. 31, and has moved far enough on its out- 



THE PISTON-VALVE. 



45 



ward stroke to just close the admission-port. Fig. 34 repre- 
sents the piston as having moved a little further in the 
stroke after the cut-off occurred or under expansion. The 
valve is now beginning to open the admission-port to the 
exhaust and at the same time has just closed the port (at the 
right in the drawing) through which steam has been exhaust- 
ing during the forward stroke of the piston, thus producing 
compression. The difference in the position of the piston in 




Fig. 33. 

Figs. 33 and 34, represents the distance the piston moved 
under expansion. 

Having now a fair understanding of the operation and the 
position of the valve relative to that of the piston at various 
points in the stroke, we will consider a method of setting a 
piston-valve of the type just explained. First, place the 
eccentric on the dead-center next to the cylinder and with 
hammer and prick-punch make a punch mark on the valve- 
stem near the valve-stem guide and a similar mark on the 
guide itself and with a pair of compasses take the distance 



46 



THE PISTON-VALVE. 



between the two punch marks. The object in making punch 
marks upon the valve-stem before commencing operations is 
for the purpose of enabling the engineer to return the several 
parts to their original position should occasion demand it, and 
a fresh start made, which would be found difficult to accom- 
plish when the edges of the valve and steam ports cannot be 
easily seen as in the case of the piston-valve. It may be 
well to remark here that it is a good plan to mark the various 
parts of any machine before attempting to take it apart and 




Fig. 34. 



especially so when one is not sufficiently familiar with the 
mechanism in hand to know the exact position each part 
should occupy and the relation of each part to the others. 

We are now ready to disconnect the valve-stem from the 
guide-block. This done, take off the back chest-cover and 
pull out the valve and stem, then take off the other chest- 
cover. Next make a template of thin sheet iron or steel 
about an inch wide and make the length of the template 
equal to the thickness of one of the pistons of the*valve 
plus the lead, as shown in Fig. 36. With a scriber in one 



THE PISTON-VALVE. 



47 



hand place one end of the template against the inner side of 
the port and with the scriber make a fine mark or line at the 
other end of the template as shown in Fig. 37. Repeat the 
operation at the opposite end of the chest. Now place the 
valve in the chest and slip the inner chest-cover on the 
valve-stem and connect the latter to the guide block, bringing 
the punch marks to their original position with the compasses. 




Before attempting to set the valve, we must first adjust the 
length of the eccentric-rod to the proper length, which is 
accomplished by turning the eccentric first to one dead-center 
and then the other, seeing that the outer edges of the valve 
open the ports to an equal amount when the eccentric occupies 
these positions. In observing the operation of the piston- 
valve in the foregoing explanation, we found that the direc- 
tion of the valve travel was ofifiosite to that of the piston when 
the latter was at or near the dead-centers, therefore, after 
niacins: the crank on the dead-center nearest the cylinder. 



THE PISTON-VALVE. 



turn the eccentric on the shaft in the o^osite direction to 
that in which the engine is to run, until the outer edge or end 
of the valve just coincides with the fine line drawn on the 
valve-seat farthest from the crank. The inner edge of that 
piston of the valve will then have opened the steam port to 
the amount of the lead. Fix the eccentric to the shaft and 
turn the crank to the opposite dead-center when the outer 





Fig. 36. 



Fig. 37. 



edge of the valve (at the opposite end of the chest) should 
coincide with the line drawn on the valve seat. 

If it does, then the inner edge of that piston of the valve 
also opens the steam port to the amount of the lead. Re- 
place the chest covers and the job is finished, but whether it 
will remain " finished " or not when the engine is started up 
under steam is another question and one difficult to answer 
until the engineer's friend, the indicator, is called upon for a 
card which is equivalent to a mirror, reflecting the work of 
the valve with ideal clearness and accuracy. 



THE CENTRIFUGAL SHAFT-GOVERNOR. 49 

The Centrifugal Shaft-Governor* 

How it Effects the Distribution of Steam* 

Owing to the multitude of designs of automatic shaft- 
governors now in use, many of which are, in operation, 
exactly alike, differing only in minor detail — the same general 
principle being embodied in each — it becomes impracticable 
to attempt to describe all forms of shaft-governors, therefore 
we will confine ourselves to the principle of the shaft -governor 
upon which the majority of governors are designed. 

In the first place let us consider the practical operation of 
the movable eccentric used in connection with the shaft- 
governor. Some engineers claim that the " throw " of an 
eccentric is equal to the eccentricity of the eccentric while 
others (probably the majority) claim that the throw is equal 
to the distance the eccentric is capable of moving the valve, 
without multiplying mechanism interposed between the ec- 
centric and valve. As the latter definition is usually accepted 
among engineers as the more nearly correct we will here 
consider the " throw " of an eccentric as being equal to the 
distance the latter is capable of moving the valve, or as 
being equal to the valve-travel. The diameter of an eccentric 
usually suggests the extent of the "throw," namely, when we 
hear of an eccentric two feet in diameter, it immediately 
suggests a very long valve-travel, and when we hear of a 
100-h. p. engine having eccentrics of four or five inches in 
diameter, it usually suggests a short valve-travel, and, while 
these inferences may prove to be correct in many instances 
yet the diameter of an eccentric really has nothing to do with 



So 



THE CENTRIFUGAL SHAFT-GOVERNOR. 



its throw or the distance it is capable of moving the valve, 
that is, within certain limits. 

This may be understood by referring to Fig. 38 which 




represents an eccentric-disc or "block" as it is often called, 
in which the eccentricity is zero. 

Now, in this case, it would make no difference whether 
the diameter was ten feet or ten inches, the throzv will stil! 



THE CENTRIFUGAL SHAFT-GOVERNOR. 5 1 

be zero. From this we see that the throw of an eccentric is 
dependent upon the amount of eccentricity given it, which is 
measured by the distance between the center of the eccentric 
and the center of the shaft. Referring to Fig. 39 we find an 
eccentric-block of the same diameter as in Fig. 38, but the 
eccentricity is now. apparent and is measured by the distance 
between the points b and c, and if the eccentric should be 
turned to the position shown in Fig. 40, or one-half revolution^ 
it would have moved the valve a distance equal to b d, which 
is twice the distance of b c, therefore the throw of an eccentric 
as we are considering it, is equal to twice its eccentricity, or 
twice the distance between the center of the eccentric and 
the center of the shaft. In Fig. 41 the diameter of the ec- 
centric is the same as before, and the eccentricity is measured 
between the points e f 9 which is about one-half the distance 
of b c in Fig. 39. 

Now, if this eccentric should be turned to the position 
shown in Fig. 42 or one-half revolution, the eccentric would 
have caused the valve to move a distance equal X.o f g, or 
twice its eccentricity, but the valve would have moved but 
one-half as far as in Fig. 40. The eccentricity of the eccen- 
tric in Fig. 41 has been diminished, that is, the distance 
between the center of the eccentric and the center of the 
shaft has been lessened, therefore we see that the throw of 
an eccentric depends upon the distance between the center 
of the eccentric and the center of the shaft and that when 
this distance is diminished the travel of the valve is shortened. 
The duty of the governor-weights and their connecting levers 
is to diminish the eccentricity of the eccentric and this is 
accomplished by moving the eccentric across the shaft. Fig. 



52 



THE CENTRIFUGAL SHAFT-GOVERNOR. 



43 represents the position of an eccentric at the commence- 
ment of the stroke of the piston. It is represented as having 
" angular advance," which has caused the valve to move from 
its position of mid-travel to that shown. The valve has now 
opened the admission port to the amount of the lead. Fig. 44 
represents the eccentric as having been moved a certain 




distance across the shaft, and it will be noticed that the 
distance between the center of the eccentric and the cen- 
ter of the shaft has been diminished to about three-fourths 
of that shown in Fig. 43 and the travel of the valve will also 
be three-fourths of that in Fig. 43. The foregoing illustrates 
the principle involved in the operation of a shaft-governor 
and shows the manner in which the governor-weights effect 
the valve-travel. It will now be noticed that the center 



THE CENTRIFUGAL SHAFT-GOVERNOR. 53 

line of the eccentric inclines further to the right in Fig. 
44 than in Fig. 43, showing that diminishing the eccentricity 
of the eccentric (and therefore the valve-travel) has had the 
effect of increasing the " angular advance," for turning to the 
valve in Fig. 44, we find the lead greater than in Fig. 43. 
This illustrates the fact that in this form of governor (which 
represents in principle a very large number of those in use) 
when the distance between the center of the eccentric and 
the center of the shaft is diminished the lead is inc?-eased, 
and in many instances this proves to be an advantage, while 
in others it is very doubtful if any material benefit arises 
therefrom. 

The cause of this increase in lead is due to the fact that 
the center of the eccentric when moved across the shaft 
describes an arc of a circle the center of which is at s. Until 
within a comparatively short time, the above result was 
obtained in all shaft -governors, viz., the lead increased as the 
travel of the valve was shortened, but today there are several 
forms of shaft-governors so constructed that the lead remains 
constant for all positions of the eccentric, and consequently 
for all lengths of valve-travel within the limits of the governor. 

One of the most common methods of obtaining constant 
lead for various lengths of valve-travel is illustrated in Fig. 45. 

In this type of governor the eccentric is moved straight 
across the shaft as indicated instead of describing an arc of a 
circle as previously mentioned. Fig. 45 shows the position of 
the eccentric when in " full gear," or the position correspond- 
ing to latest cut-off — earliest cut-off and an intermediate 
position being shown in the central figure. 

We are now prepared to consider the effect upon the 



54 THE CENTRIFUGAL SHAFT-GOVERNOR. 

points of cut-off, release (or exhaust) and compression, and 




also upon the period of expansion, due to shortening the 
valve-travel. We will first consider the above points of cut- 



THE CENTRIFUGAL SHAFT-GOVERNOR. 



55 



off, release, etc., in an engine, say when starting and before 
the speed has increased sufficiently to cause the governor- 




weights to move outward, or before the governor has effected 
the length of the valve-travel. Fig. 46 represents the position 



56 THE CENTRIFUGAL SHAFT-GOVERNOR. 

of the piston, valve, and eccentric at the commencement of 
the stroke. 

The valve has now opened the admission port to the 
amount of the lead, the opposite port is open a little to the 
exhaust, which opening measures the amount of exhaust lead. 

Fig. 47 represents the admission port as wide-open, the 
eccentric having reached the dead-center, farthest from the 
cylinder, while the piston has moved to about one-third 
stroke. Fig. 48 shows the relative position of the piston, crank 
and eccentric at the point of cut-off, which occurs at about 
two-thirds stroke. Fig. 49 represents the piston as having 
moved a little further in the stroke after cut-off occurred, or 
under expansion. 

The valve has now just closed the exhaust (at right in 
drawing), thus producing compression which occurs at about 
nine-tenths stroke. The admission port (at left in drawing) 
is now open a very little to the exhaust, the piston in its 
present position marking the point of release also. Let us 
now consider the effect of reducing the valve-travel which is 
accomplished by the governor in the manner previously 
described. Fig. 50 represents the position of the piston, 
valve and eccentric at the beginning of the stroke. 

The valve has now opened the admission port to the 
amount of the lead which is greater than in Fig. 46 as is also 
the amount of exhaust lead. 

Fig. 51 represents the position of the piston, valve and ec- 
centric when the admission port is wide open, or as far as can 
be opened with the present reduced valve-travel, the eccentric 
having reached the dead-center farthest from the cylinder as 
before, while the piston has moved to about one-fourth stroke* 



THE CENTRIFUGAL SHAFT-GOVERNOR. 



57 



Fig. 52 represents the position of the foregoing members at 
the point of cut-off which now occurs at one-half stroke 
instead of two-thirds stroke as in the preceding case. Fig. 
53 shows the piston as having moved further in the stroke, 
and after the cut-off occurred, or under expansion. 




Fig. 53- 

The period of expansion is now greater than in Figs. 48 and 
49. The valve has now closed the exhaust port (at right in 
drawing) producing compression, which now occurs at seven- 
eighths stroke instead of nine-tenths stroke as in Fig. 49. The 
present position of the piston (Fig. 53) also marks the point 
of release which occurs earlier on the return stroke than in 
the preceding illustration. 



5^ SETTING A LINK-MOTION. 

Finally, the shaft-governor changes the point of cut-off by 
shortening the travel of the valve, and this, by lessening the 
distance between the center of the eccentric and the center 
of the shaft which is accomplished by moving the eccentric 
across the shaft. 

The effect of shortening the travel of the valve is: First, 
in increasing the lead, both steam and exhaust; second, in 
diminishing the port opening for the admission of steam to 
the cylinder; third, in producing an earlier cut-off, thus in- 
creasing the period of expansion; fourth, in causing ; the point 
of release to occur earlier in the forward stroke and also a 
reduction in the port opening for the exhaust steam to escape 
from the cylinder; and lastly, in causing the point of com- 
pression to occur earlier on the return stroke, thus entrapping 
a larger volume of exhaust steam in the cylinder which in- 
creases the pressure of compression, 

Setting a Link-Motion* 

The types of valve-gears which have been illustrated, 
comprise those generally used on stationary engines. The 
link-motion, however, is. used principally on locomotive, 
marine and hoisting engines, and also on some makes of 
portable (traction) engines. 

The movable-link or link-motion is, in itself, a very simple 
mechanism, and in operation it is equally simple and presents 
one of the best forms of adjustable valve-gear as well as 
reversing gear. Those who have been successful in compre- 
hending the operation of a slide-valve actuated by a single 
eccentric as illustrated in previous chapters will readily 



SETTING A LINK-MOTION. 



59 



understand the operation of the link-motion by referring to 
Figs. 54, 55, 56, 57, which represent the relative positions 
of the various members of which a link-motion is comprised. 
Notwithstanding the simplicity of the link-gear in con- 
struction, as well as operation, the problems met with in 
designing a link-gear and the points to be considered when 
setting the same are, respectively, as difficult and as many as 
in almost any other form of valve-gear. 




Fig. 54. 

Engineers are seldom, if ever, called upon to design a 
link -gear; therefore, we will turn our attention to the work of 
setting the same, as this information is of much importance 
to men in the shop as well as the engine-room. 

But, before we begin the work of setting the eccentrics, it 
may be to the interest of some of us to obtain the names of 
the various members of a link-motion. Fig. 54 represents 
this form of valve-gear as applied to locomotive, hoisting and 
portable engines (in marine gears the rocker-shaft is usually 
dispensed with), in which 1 is the valve, 2 the valve-stem, 3 



60 SETTING A LINK-MOTION. 

the rocker-shaft, 4 the link, 5 the link-block, 6 the saddle, 7 the 
saddle-pin (or hanger stud), 8 the link-hanger, 9 the tumbling- 
shaft, 10 the reach-rod, 11 the forward eccentric with strap, 12 
the forward eccentric-rod, 13 the backing (or back) eccentric 
with strap, 14 the back eccentric-rod. 

The terms "forward" and "backward" and forward ec- 
centric and backing eccentric, when applied to the gear of a 
stationary engine do not convey a very definite idea of the 
direction in which the engine will run when corresponding to 




Fig. 55. 

either eccentric. It depends largely upon the direction re- 
quired in the machinery being driven as to which will be 
respectively the forward and backing eccentric. Engineers, 
however, when setting a link -gear usually consider the engine 
aside from the machinery being driven, and when so con- 
sidered, the direction corresponding to forward and backward, 
respectively, is the same as in the locomotive, namely — when 
the engine runs " under " it is said to be running forward or 
ahead, and when running "over" it is said to be running 
backward or backing. The meaning of the terms " over " and 



SETTING A LINK-MOTION. 6l 

"under" were described in a previous chapter, together with 
a rule for ascertaining the direction in which any engine runs. 
In marine engine practice the terms employed to designate 
the direction in which the engine runs, are " ahead " and 
"astern." The eccentric actuating the valve when the vessel 
moves ahead is called the forward eccentric.and the eccentric 
actuating the valve when the vessel moves backward or 
astern is called the backing eccentric. In the locomotive of 
the present design the forward eccentric-rod is attached to 




Fig. 56. 

the upper end of the link, and the rod of the backing eccen- 
tric is attached to the lower end of the link, therefore, in 
stationary engine practice, it is customary to connect the rod 
of the eccentric which causes the engine to run "under" to 
the upper end of the link and the rod of the eccentric causing 
the engine to run " over " to the lower end of the link. This 
applies to gears in which a rocker-shaft is employed of the 
type shown in the drawings. A link -gear without rocker-shaft 
will be considered later. 

With the foregoing points well established in our minds 



62 SETTING A LINK-MOTION. 

we shall find the work of setting a link-motion much more 
simple than some engineers would have us suppose. 

Before attempting to set the eccentrics we will first set the 
upper arm of the rocker in a vertical position — plumb. The 
valve should now occupy the position of mid-travel; that is, 
the outer edges of the valve should extend an equal distance 
beyond the outer edges of the steam-ports. This position 
may be readily obtained by measuring the length of the 
valve and from this distance subtract the distance between 




Fig. 57. 

the outer edges of the steam-ports. Divide the remainder 
by two and lay off the quotient from the outer edge of the 
steam-port. When the upper arm of the rocker is plumb, the 
edge of the valve should coincide with this line. This opera- 
tion gives us the proper length of the valve-stem. Place 
the reversing lever in position of full forward gear. In the 
method of setting a link-motion which follows, the same 
starting point is observed as in all previous cases, namely; 
the crank and the full side of both eccentrics are turned to 
the dead-center nearest the cylinder. When occupying this 



SETTING A LINK-MOTION. 63 

position the valve, rocker-shaft and the centers of the eccen- 
trics (which are represented by round dots) will be in the 
position shown in Fig. 58. 

We will first set the forward eccentric. 

It will be remembered that, when an engine runs forward 
it runs " under," which is in the direction of the arrow, see 
Fig. 58, and the rocker-shaft is of the type that reverses the 
motion or direction of the valve relative to that of the eccen- 
tric, therefore we turn the eccentric in the offosite direction 




Fig. 58. 

to that corresponding to " forward " until the valve leaves the 
steam-port open to the amount of the lead, when the various 
members will occupy the position shown in Fig. 59. 

Tighten the set-screws in this eccentric. 

Now, throw the reversing lever into the position of full 
backward gear. This operation will raise the link and bring 
the rod of the backing eccentric in line with the link -block 
and the valve will then occupy the same position as in 
Fig. 58. 

When an engine runs backward, it runs "over" and ob- 



64 



SETTING A LINK-MOTION. 



serving the same rule as before, we turn the backward eccen- 
tric " under " until the valve leaves the same steam-port open 
to the amount of the lead. 

Throw the reversing lever into the position of full forward 
gear again, when the valve will occupy the position shown in 
Fig. 60; also the eccentric centers. In a link -gear which has 
been properly designed and well adjusted, the valve should 
occupy the same position over the ports, whether the link is 




Fig. 59. 



in full forward or full backward position — the crank being on 
the dead-center. 

Now turn the crank to the back dead-center and measure 
the amount of the lead which will seldom be the same as it 
was when the crank occupied the forward center. Sometimes 
the lead will be greater when on the back center, and at other 
times there will be no lead at all, the valve being what engi- 
neers call "blind." 

We will assume that the lead has been measured with the 
crank on both the forward and back centers. When on the 



SETTING A LINK-MOTION. 65 

forward center it was three-thirty-seconds of an inch, and 
when on the back center the valve was blind. This indicates 
that the forward eccentric-rod is too long and must be short- 
ened an amount equal to one-half the difference in the lead as 
obtained on both centers, which would be three-sixty-fourths 
of an inch. 

Put the reversing lever in position of full backward gear, 
engine still on back-center and measure the lead, then turn to 
the forward center and again measure the lead. If in the lat- 




Fig. 60. 

ter position it is found to be too great, it indicates that the 
backing eccentric-rod is too long and must be shortened an 
amount equal to one-half the difference in the lead when the 
crank occupies either center. 

The work of equalizing the lead may necessitate turning 
the engine from one center to the other several times in both 
forward and backward gear, but when the equalization is ac- 
complished, the link-motion will have been correctly set as 
far as the lead is concerned. • ' 

In the foregoing directions, the proper place for the revers- 



66 



SETTING A LINK-MOTION. 



ing lever when beginning the work of setting the eccentrics 
was given as full forward and full backward gear respect- 
ively. 

Upon this point in setting a link -gear engineers do not 
agree. Some prefer to place the reversing lever in the 
position it usually occupies when the engine is running and 
set the eccentrics with the reversing lever in this position. 
Others select the full gear position which is undoubtedly to 
be preferred when the link is used for reversing the direction 
of the engine only, the s$eed being governed by a governor. 
When setting a link -gear, however, the method to be adopted 
should be governed by the running qualities produced, that is 
to say, if an engine runs smoother when " hooked back" (the 
eccentrics having been set in full gear) then the valve should 
be re-set with the reversing lever in the running position and 
vice versa. 



Forward Gear. 


Am't of Lead 


Forward Center. 


Am't of Lead 


Back Center. 


Too Much. 
Not Enough. 


Shorten forward rod. 
Lengthen forward rod. 


Too Much. 
Not Enough. 


Lengthen forward rod. 
Shorten forward rod. 


Backward Gear. 



Am't of Lead 



Too Much. 
Not Enough. 



Forward Center. 



Shorten backing rod. 
Lengthen backing rod. 



Am't of Lead 



Too Much. 
Not Enough. 



Back Center. 



Lengthen backing rod. 
Shorten backing rod. 



SETTING A LINK-MOTION. 67 

The accompanying table contains in condensed form, the 
foregoing directions for adjusting the length of the eccentric- 
rods when equalizing the lead, and may be readily compre- 
hended by referring to the drawings. The amou?it either rod 
is to be lengthened or shortened is given in the preceding 
lines. 

Having set the eccentrics and equalized the amount of lead, 
tho same operations must be repeated at the opposite side of 
the engine, assuming that it is a double engine with cranks set 
at right angles or at 90 degrees as in the locomotive and most 
types of hoisting engines. In small engines the work of setting 
the valves usually ends with equalizing the lead, but in engines 
with cylinders of the size of those in locomotives or larger, we 
must go a step farther and equalize the cut-off for it is important 
that about the same amount of steam should be admitted to 
each cylinder and to each end of the cylinders. The angularity 
of the connecting-rod tends to give a greater supply of steam 
to the forward end of the cylinder, and in a new and well- 
designed gear, this inequality is usually very nearly corrected 
when designing the gear by locating the hanger-stud a very 
little back of the center of the link (see Fig. 54). Before we 
begin operations it might be well to state 'that when the link- 
gear is used for reversing only, the reverse-lever is usually 
placed in full gear forward and back when setting and ad- 
justing the valves, but when the engine is usually run with the 
link hooked up, place the reversing lever in that notch, for- 
ward and back, in which it is usually kept when the engine is 
running. For the purpose of illustration and simplicity we will 
assume that the link is used for reversing only. First place 
the reverse-lever in position of full forward gear and turn 



68 SETTING A LINK-MOTION. 

the crank to the exact dead-center nearest the cylinder. 
The valve will now have opened the port at the head-end of 
the cylinder to the amount of the lead. Now have the engine 
turned forward (" under") slowly. 

The valve will be seen to open the port until the cross-head 
reaches nearly one-half stroke, when it will begin to return 
and close the port again and until cut-off is reached. At this 
point the engine must be stopped. Measure on the guide the 
distance the cross-head has moved from the end of the stroke 
and make note of it. Then have the engine turned in the 
same direction and obtain the cut-off for the forward stroke 
in the same manner and make note of this also. Find the 
points of cut-off in the other cylinder in precisely the same 
manner. 

Suppose one engine to be 10 inches by 20 inches and that 
on the forward stroke on one side the valve admits steam to 
say 16 inches and on the opposite side to 17 inches of the 
stroke. This inequality may be corrected by lengthening one 
link-hanger and shortening the other ; in other words, the 
hanger on the side cutting off at 16 inches must be lengthened, 
and the one on the side cutting off at 17 inches must be short- 
ened. If the discrepancy is less than that given in this size 
of engine the short side only may be lengthened. The amount 
of adjustment to be given the hangers can only be had by 
trial. As link -hangers are seldom provided with means for 
adjusting their length, it will be found more convenient to 
move the arms on the tumbling-shaft. When both arms are 
to be moved on the tumbling-shaft, it is better to mark the 
position of the link on the short side. Lengthen or lower this 
side the whole amount necessary, then raise it to one-half this 



SETTING A LINK-MOTION. 69 

amount and raise the opposite link an amount equal to one- 
half the whole distance required in the first link. Equalizing 
the cut-off for both strokes in the same cylinder is a harder 
undertaking. 

In new work, as stated, this inequality may be overcome 
by the saddle stud but in merely resetting this will not be 
admissible. 

Supposing that in our cylinder the cut-off occurs at 15 
inches on the backward stroke and at 16 inches on the forward 
stroke, we must first endeavor to locate the cause of the 
trouble. 

Examine the rocker-arms to ascertain whether they are 
not sprung. If all right, examine the link which may be 
sprung out of its true radius. 

In all cases ascertain the condition of the joints that the 
difficulty may not be due to lost motion. 

Where it is impracticable to remedy the discrepancy by 
correcting the origin of the trouble it may be accomplished 
in other ways. If the inequality is very slight it may be 
remedied by throwing out the back motion or by lengthening 
or shortening the valve-stem when the valve is in the position 
of mid-travel. It very often happens that the equality of lead 
opening must be sacrificed to obtain equality of cut-off. 

It may be well to state that with a distorted link-motion 
the changes necessary to obtain a correct adjustment 0/ the 
various members cannot be expected the first time trying by 
one who has had little or no experience in such work. Even 
with experienced men it is often a case of " try, try again." 
In the link-motion, and in fact in valve-gears of any kind 
having as many unadjustable working joints as the link- 



70 SETTING A LINK-MOTION. 

gear, considerable trouble is often experienced from lost 
motion when endeavoring to equalize the movements of 
the valve. These difficulties however may be very easily 
remedied as follows : When moving an eccentric from the 
dead-center to the required position, move it a little beyond 
and then back to the correct position. When equalizing the 
lead and cut-off it is necessary that the lost motion be taken 
up, and this may be done by allowing the crank-pin to move a 
little beyond the center and then back to the exact dead- 
center. 

It sometimes happens that an engineer is required to 
reset a valve during working hours owing to an eccentric 
slipping on the shaft or other reasons; therefore, it is a good 
plan to have an emergency method of setting the valves and 
without removing the steam-chest cover. We will assume 
now that the eccentrics have been set and the final adjust- 
ments made with the steam-chest cover off as given in the 
foregoing lines. Before replacing the steam-chest cover, 
place the reverse-lever in full forward gear and turn the 
crank to the dead-center nearest the cylinder, taking up the 
lost motion in the manner explained. With hammer and 
prick-punch make a punch mark on the stuffing-box (not the 
gland) as at A, Fig. 61. 

Now, before moving the engine procure a piece of steel 
wire, say three-sixteenths or one-fourth of an inch in 
diameter, and long enough to make a tram of the form shown 
in Fig. 61. Grind the ends to a sharp point and bend them 
down as shown making one leg a little longer than the other. 
After making the tram place one leg in the punch mark at A 
and with the other make a fine line on the valve-stem. 



SETTING A LINK-MOTION. 



71 



On this line make another punch mark as shown at B. 
Turn the engine ahead (under) until the crank reaches the 
back center, and after taking up the lost motion as before, 
again place the short leg of the tram in the punch mark on 




Figs. 61, 62 and 63. 

the stuffing-box and with the long end make a fine line on 
the valve-stem as before and on this line put a punch mark 
as at C, Fig. 62. Now divide the distance between the punch 
marks B and C and in the center place a third punch mark as 
at D. 



*J2 SETTING A LINK-MOTION. 

The mark Z) is to be used when we wish to place the 
valve in the position of mid-travel as shown in Fig. 63, which 
position becomes necessary when adjusting the length of the 
valve-stem. 

To set the valve by means of the punch marks the engine 
is first placed on the center nearest the cylinder and the full 
side of the eccentric to be set, the same. Place the reverse- 
lever in position of full forward gear (if the forward eccentric 
is to be set or full back gear if the back eccentric is to be set) 
and with tram in hand, have the slipped eccentric turned in 
the proper direction until the punch mark B (punch mark C 
for back gear) reaches the long leg of the tram as shown in 
Figs. 61 and 62 respectively. Have the eccentric fixed at 
this point and the engine will be ready to start. These punch 
marks may be used for the purpose of equalizing the cut-off 
also, by first placing the crank in the same position as for 
setting the eccentrics, then have the engines turned ahead 
when the mark B on the valve-stem will be seen to move 
away from the tram until the cross-head has reached nearly 
one-half stroke, when it will return to the point of the tram, as 
in Fig. 61. This marks the point of cut-off and the distance 
the cross-head has moved away from the end of the stroke 
represents the distance that steam is admitted to the cylinder 
before cut-off occurs. 

The same operation is repeated for the forward stroke 
starting from the back center and using the punch mark C. 
Then place the reverse-lever in position of back gear and 
proceed in precisely the same manner, to find the point of 
cut-off when the engine is backing. 

There are certain peculiarities observed in the operation 



SETTING A LINK-MOTION. 



73 



of a link-motion and certain terms used in connection there- 
with, an explanation of which may not be without interest. 

The first is the crossing of the eccentric-rods when the 
crank occupies the back center. 




— e--r-D 



B 



This position of the rods may be readily understood by 
referring to the centers of the eccentrics which are located at , 
the extremities of the heavy lines indicating the position of 
the full part of the eccentric. In Fig. 64 the centers of both 
eccentrics are between the centers of the shaft and the link* 



74 SETTING A LINK-MOTION. 

the center of the forward eccentric is above and that t 
back eccentric is below the center of the shaft. 

The rod from the forward eccentric is attached to the 
upper end of the link, and the rod from the back eccentric is 
attached to the lower end of the link. Fig. 65 represents the 
crank (and shaft) as having made one-half revolution and 
the centers of the eccentrics are on the opposite side of the 
center of the shaft from the link, the center of the back 
eccentric is now above the center of the shaft and that of the 
forward eccentric is below the center of the shaft, and, as the 
outer ends of the eccentric-rods are attached to the same 
ends of the link as in Fig. 64, it is evident that they must be 
crossed when the crank occupies the back center. 

It is well known among engineers that the lead of a valve 
operated by a link -gear increases as the link is " hooked up," 
that is, as the link is raised and the link -block approaches the 
center of the link as in Fig. 64. This position of the link is 
known as mid-gear. 

The cause of the increase in .ead as the link approaches 
mid-gear may be understood by first referring to Fig. 64, 
which represents the relative position of the link and eccen- 
trics when the crank is on the forward center. The centers 
of the eccentrics are a certain distance ahead of the center 
of the shaft, or line A B. When the link is moved up or 
down, each eccentric-rod pin (in the link) describes an arc of 
a circle, the radius of this arc being equal to the distance 
between the centers of the eccentric-rod pins and the center 
of the eccentrics. The link is influenced directly by one or 
the other of the eccentrics, regardless of the position in the 
link occupied by the link -block. In Fig. 64 the link-block 



SETTING A LINK-MOTION. 75 

Stands at its farthest point away from the shaft or axle, and 
the lead opening is therefore the greatest. 

If the link be now lowered, the backing eccentric-rod will 
begin to pull the link back, and, as the forward eccentric-rod 
approaches the central line of motion C £> 9 it will also draw 
the link back so that when the link and block occupy the 
position of full gear the lead opening will be less. When the 
crank-pin is on the back center as in Fig. 65, the eccentric 
centers will be on the opposite side of the center of the axle 
(line A B) and the rods will be crossed as explained above. 
When in this position with the link -block in mid-gear, the 
latter is closer to the axle or shaft than it would be in any 
other position of the link, and consequently the lead opening 
is greatest. If the link be now lowered, the forward eccentric- 
rod will approach a horizontal position — pushing the link 
(and link block) away from the axle, reducing the lead opening. 
Raising the link from a position of mid-gear to full backward 
gear has a similar effect with the crank -pin on either center 
It both eccentric-rods were worked from a common center, 
viz., the center of the shaft or axle, then the link could be 
raised or lowered when the crank occupied either center 
without moving the link -block. 

Short eccentric rods will increase the tendency toward 
greater lead opening as the link -block approaches the center 
of the link. 

Increasing the throw of the eccentrics has the same effect, 
as it throws the centers of the eccentrics farther apart and 
hence farther to one side or the other of the line A B. 

Slip of the Link. 

As the link-biock receives the pin in the lower rocker-arm, 



76 



SETTING A LINK-MOTION, 



the block moves through the same arc of a circle as the pin 
which is nearly straight or horizontal — see the upper arm of 
the rocker shaft in Figs. 66, 67 and 68. The saddle-stud being 
located a little back of the center of the link, together with 
the action of the eccentric rods, causes the link to move 
slightly in a vertical direction at certain parts of the stroke, 
thus causing the link to sli$ on the link -block. 




r©v 




Fig. 66. 



Fig. 67. 



Fig. 68. 



Figs. 66 t 67 and 68 represent the slip of the link. The 
drawings, however, show a greatly exaggerated case for the 
purpose of more clearly illustrating the meaning and cause of 
" slip." We will now consider the relative positions of the 
various members of a link -gear when setting the gear without 
a rocker-shaft. We will assume that the engine is to run in 
the same direction relative to the position of the link as 
before, that is, when the link is down the engine is to rup 



SETTING A LINK-MOTION. JJ 

under and vice versa. The eccentric-rods have the same 
names as before, viz., the one attached to the upper end of the 
link is the forward eccentric-rod, and that attached to the 
lower end of the link, the back eccentric-rod. When the link 
is down. therefore it is said to be in full forward gear. After 
placing the link in this latter position, turn the crank and full 
sides of both eccentrics to the dead-center nearest the cylinder 
as shown in Fig. 69. As there is no rocker shaft in this case f 
the direction of the engine will correspond to the direction in 
which the eccentrics are turned. We wish the engine to run 
forward (under) when the link is down, therefore we turn the 
forward eccentric in the same direction we wish the engine to 
run., viz., under and until the valve opens the forward port 
to the amount of the lead. The several parts will then occupy 
the positions shown in Fig. 70. Fix the forward eccentric to 
the shaft, then place the reverse-lever in position of full 
back gear. This will raise the link to the position shown in 
Fig. 71, and again open the back port. 

Now, when the engine runs backward it is to run over, 
therefore we turn the back eccentric in the same direction the 
engine is to run as before, this time turning it " over" until the 
valve opens the forward port to the amount of the lead as 
before. The several parts will then occupy the positions shown 
in Fig. 72. Again place the reverse lever in the position of 
full forward gear and note the lead opening. If it has been 
changed by setting the back eccentric, move the forward 
eccentric a trifle to equalize the lead, then fix both eccentrics 
to the shaft. 

The next operation is to equalize the lead between the 
forward and back centers and in both forward and back gear, 



?8 f 



SETTING A LINK-MOTION. 




SETTING A LINK-MOTION. 79 

in the same manner as previously described except that as* 
the present type of gear has no rocker shaft, the direction of 
the valve will be the sa?ne as that of the eccentric actuating 
it, therefore the directions given in connection with the previ- 
ous type of link gear in the form of a table must be reversed 
when applied to a gear without a rocker-shaft. The equali- 
zation of the cut-off is accomplished in this gear in precisely 
the same manner as in a link -gear having a rocker-shaft. 

Before concluding the setting of a link-motion there is 
another problem sometimes met with in connection with this 
work and that is, placing the crank on the dead-center (for 
the purpose of setting and adjusting valves) when the axis of 
the cylinder is above the center of the crank -shaft or axle. 
In the present locomotive practice, this very often becomes 
necessary, and sometimes in connection with semi-portable 
hoisting engines. Should a job of this kind present itself, 
obtain a good sized piece of paper or a smooth board large 
enough to receive a diagram as shown in Fig. 73, which is tc 
be drawn to scale and as large as possible. 

Suppose the axis of the cylinder is two inches above the 
center of the axle. First draw the line a b, representing the 
axis of the cylinder, then draw the line c d parallel to a b. 
Set the compasses to the length of the crank (the center of 
the axle to the center of the crank-pin), and with one 
leg placed on the line c d at e, describe the circle as 
shown which represents the path of the center of the 
crank-pin, e representing the center of the axle. Next, 
set ,the compasses to the length of the connecting-rod 
plus the length of the crank, and with one leg placed at e 
describe the arc 71 o, cutting the line a b as shown. Now set 



8o 



SETTING A LINK-MOTION. 



the compasses to the length of the connecting-rod minus the 
length of the crank and with one leg placed at e, describe the 
arc P Q. From the point of intersection of the arc n o, and the 
line a b, draw the line R through the points and from the 
point of intersection of the arc P Q and the line a b, draw the 
line S through the point e and extend it through the circle as 
shown. The points where the lines R and S respectively cut 



6^ 




Fig. 73. — {Completed on opposite fag e). 



the circle will represent the true forward and back dead 
centers. 

Having found the true dead centers, the crank-pin may be 
brought to these points in the following manner : If the floor 
close to the crank is level (both ways) all well and good, but 
if not, a straight, smooth board should be levelled close to the 
• crank and on the floor. With a bar and trammel point, 
obtain the distance between the floor (or board) and the cen- 
ter of the axle. Measure on the drawing the distance from 



SETTING CORLISS ENGINE VALVES. 8l 

the line c dto the point where line R cuts the crank-pin circle 
and raise the trammel point on the bar to the same (actual) 
distance— having previously marked the first position of the 
trammel point on the bar. Have the crank turned to the 
forward center, or close to it, and then with one end of the bar 
on the floor (or board) have the crank turned slowly until the 
center of the crank-pin comes opposite the trammel point. 
The crank will then occupy the true forward center. 
Now measure the distance from the line c d to the point 




FlG. 73. — {Completed on o££o site $age) % 

when the line S cuts the crank-pin circle (the lower side of 
the circle farthest from the cylinder). Lower the trammel 
point on the bar a like amount below the first position on the 
bar. Have the crank-pin turned to the approximate back 
center and then brought to the exact position the same as for 
the forward center, when the crank will occupy the true back 
center. Lost motion should in all cases be taken up, as 
explained in connection with the setting of an eccentric. 

Setting: Corliss Engine Valves, 

The Corliss valve-gear with its releasing mechanism, differs 
materially from the types of gears already illustrated, and as 
an engineer must understand the duty of each member of a 
valve-gear before he can expect to successfully adjust it, 



82 



SETTING CORLISS ENGINE VALVES. 



it may be well first to consider the construction and operation 
of a Corliss valve-gear. 

The exhaust-valves in a Corliss engine are, in operation, 
the same as the semi-rotary valves. The exhaust valves 




Fig. 74. 

receive motion from the wrist-plate by means of the rods con- 
nected to it, and a single crank-arm fixed on the outer end of 
the valve-stem as shown in Fig. 74. 

The drawings illustrate the exhaust-valve mechanism in a 



SETTING CORLISS ENGINE VALVES. 



8.3 



sufficiently clear manner to render further explanation unnec- 
essary. 

The mechanism employed to open and release (close) the 
steam-valves embraces the most important features of a Cor- 
liss valve-gear. On the valve-stem and next to the yoke is 
placed a bell-crank lever, A Fig. 75. At the end of the hori- 
zontal arm of the bell-crank lever is the hook, B, which works 




C^ 




Fig. 75- 



Fig. 76. 



freely on the stud. On the valve-stem and placed next to the 
bell-crank lever is the disc C Fig. y6, provided with a projec- 
tion C 1 and having an upwardly extending arm to which is 
connected one end of one of the rods from the governor. At 
the outer end of the valve-stem is placed the valve-stem crank 
£>, Fig. y/ y which carries at its outer end the catch-block D 1 , 
which is engaged by the hook B on the end of the bell-crank 
lever. To the valve-stem crank D is connected the rod V 2 



8 4 



SETTING CORLISS ENGINE VALVES. 



from the dash-pot. The operation of this mechanism may be 
understood by referring to Fig. 78 which represents the va- 
rious members in the position they occupy at the commence- 
ment of the stroke of the piston. The disc, operated by the 
governor, is in a position to allow the hook to move to its 
highest position, or that position corresponding to latest cut- 
off, before being tripped by the projection C 1 , Fig. j6. 





Fig. jj. 



Fig. 78. 



It will also be noticed that the hook has engaged the catch- 
block on the valve-stem crank or arm. Now as the piston 
moves forward in the stroke, the bell-crank lever is turned, 
round on the valve-stem by the rod K } Fig. 74, from the wrist- 
plate. The horizontal arm of the bell-crank lever carrying 
the hook, together with the arm on the valve-stem begin to 
rise and continue so to do until arriving at the position shown 



SETTING CORLISS ENGINE VALVES. 



85 



in Fig. 79. By an inspection of both Figs. 78 and 79, it will 
be seen that the inner member of the hook has followed the 
periphery of the disc C, and is held in the position shown in 
Fig. 78 by the fiat spring B 1 , which keeps the hook engaged 
with the block until reaching the position shown in Fig. 79. 
As stated, the inner member of the hook follows the 
periphery of the disc operated by the governor, until arriving 
at the position shown in Fig. 79. At this point the inner arm 




Fig. 79. 



Fig. 80. 



of the hook comes in contact with the projection on the disc, 
which forces the former farther away from the center of the 
disc, and this movement also causes the hook to release the 
catch-block carried by the arm on the valve-stem. The arm 
on the valve-stem being now disengaged from the hook, is 
rapidly drawn to the position shown in Fig. 74, by the dash- 
pot and the rod Z> 2 , which causes the valve to close the steam- 
port, thus effecting the cut-off. From an inspection of Fig. 79 
it is evident that the hook is made to release the arm on the 



86 SETTING CORLISS ENGINE VALVES. 

valve-stem, when the inner member of the hook reaches the 
projection on the edge of the disc operated by the governor. 
Therefore if the disc be moved to the left, as shown in Fig. 
80, the hook can not raise the valve-stem arm to the position 
shown in Fig. 79, but releases it earlier in the upward stroke 
of the hook. As the point of release of the catch-block Z) 1 
marks the closing of the port, and as it is earlier in Fig. 80 



Fig. 81. Fig. 82. 

than in Fig. 79, it follows that the cut-off will be earlier in 
the stroke of the piston in Fig. 80 than in Fig. 79. 

The foregoing illustrations represent the operation 
of nearly all forms of Corliss gears, the differences in 
gears found on engines in use being practically in details of 
construction, the same principle of operation being embodied 
in all ; therefore it is not necessary to analyze here all forms 



SETTING CORLISS ENGINE VALVES. 



87 



of Corliss releasing gears*, for if an engineer thoroughly 
understands the construction and operation of one design, it 
will not take him many minutes to fully comprehend the 
operation of any other design, 

The mechanism shown in Figs. 81, 82 and 83 is that of the 
Reynolds-Corliss engine. Fig. 81 represents the position of 




• • Fig. 83. 

the several parts at the commencement of the stroke of the 
piston. In Fig. 83 the curved arm of the hook has engaged 
the projection on the disk operated by the governor and the 
hook has just "let go" of the catch-block, which in this case is 
carried by one of the arms of the bell-crank lever which is 
secured to the valve-stem. To the other arm is connected the 
rod from the dash-pot. Fig. 83 represents the position of the 



*For the illustrations and descriptions of the various modifications 
of Corliss engine valve-gears, see The Engineer, Nov. 15, 1899. 



88 



SETTING CORLISS ENGINE VALVES. 



several parts when the port is wide open and the hook is at 
the extreme outward end of its travel. When about to set a 
Corliss gear the first thing to be done is to " centralize" the 
various parts and equalize their movements. First, place the 
wrist-plate and rocker-arm plumb, as shown in Fig. 84, then 
with a straight edge and scriber mark the position of the 




Fig. 84. 

wrist-plate as at a and b, Fig. 85. Now turn the eccentric on 
the shaft to the dead-center farthest from the cylinder and 
make a very light mark as at c, Fig. 86, in line with the mark 
a on the wrist-plate. Then turn the eccentric to the opposite 
dead-center and in the same manner make the mark d, Fig. 
87. With a pai. of dividers or a flexible scale measure the 
distance from the mark b to the marks c and d. If the mark 



SETTING CORLISS ENGINE VALVES. 



«9 



d should be nearer b than the mark c, then the eccentric-rod 
must be lengthened a trifle. The eccentric is then to be 
placed on the dead-center as before, and measurements again 




Fig. 85. 

made. If it is then found that the marks c and d are the same 
distance away from the mark b, then the wrist-plate (mark a) 
will move an equal distance either side of the mark b t which 
proves the eccentric-rod to be of proper length. The last of 
the fine marks made on the stud represented by c and o^are 
then to be made deeper and more permanent. 



b c 



d: b c 



Fig. 86. 



"51 



nor 
Fig. 87. 



The next step is to equalize the lap of the steam valves. 
Presuming the valve-chest covers or bonnets have been re- 
moved, the end of the valve on the front side of the engine 
will appear as shown in Fig. 88 revealing the marks e, f and g. 



9 o 



SETTING CORLISS ENGINE VALVES. 



These marks are usually placed there by the builders of the 
engine when the latter is set up in the shop, but if they do 
not appear they may be made by the aid of a machinist's 
square and the table of lap of valves. 

The mark e represents the edge of the valve, /"the edge of 
the steam-port, and the distance between marks/ and g rep- 
resents the amount the valve should lap over the edge of the 




Fig. 



port when the wrist-plate stands plumb. Now, after setting 
the wrist-plate plumb by means of marks a and b, Fig. 
8$, and seeing that the hooks engage the valve arms, the 
lines e and g should be exactly in line with each other, 
at both ends of the cylinder — that is, both valves should have 
the same lap. 

If the lines do not coincide, the radial rod connected to the 



SETTING CORLISS ENGINE VALVES. 9I 

bell-crank on the steam valve-stem must be adjusted until 
the proper position of the valve is reached. 

The exhaust-valves are next to receive attention and in 
this case let c represent the edge of the valve and/ the edge of 
the port as before. If the line e is not in line with /", the valve 
must be moved until these lines coincide, which may be ac- 
complished by adjusting the right and left adjustment in the 
rod connecting that valve with the wrist-plate. The exhaust 
valve at the opposite end of the cylinder is to be set in the 
same position, and in like manner. 

Having " centralized" the valves and valve-gear, it is a 
good plan to put in the starting bar, before proceeding further 
and move the wrist-plate so that the lines a and c, Fig. 86, are 
in line. The hook of the valve to be raised should then occu- 
py the position shown in Fig. 78 and the point to be observed 
is that the clearance, or spaces h and i respectively are about 
equal. If not they may be made so by means of the right 
and left adjustment in the rod, connecting that valve with 
the dash-pot. 

By means of the starting bar open the valve, the clear- 
ance having just been equalized, until it is released. Again 
bring the marks a and c in line and again examine the 
clearance or spaces h i Fig. 78 ; if they are the same as before 
then the dash-pot at that end of the cylinder seats properly. 
The same operations are to be gone through with at the op- 
posite end of the cylinder. 

We are now ready to set the eccentric. 

Place the crank and the full side of the eccentric on the 
dead-center nearest the cylinder and drop the reach-rod on 
the stud in the wrist-plate. We will assume that the engine 



Q2 SETTING CORLISS ENGINE VALVES. 

is to run "over." Now it will be noticed by referring to Fig. 
74, that to open the steam-valve at the head-end of the 
cylinder, or the end of the cylinder farthest from the crank, 
the wrist-plate must move in the same direction as that of 
the piston, hence we turn the eccentric around the shaft in 
the same direction in which the engine is to run, and until the 
valve at the head-end of the cylinder has opened the port to 
the amount of the lead, which will be indicated by the 
position of the lines e and /"Fig. 88. Fix the eccentric to the 
shaft at this point. An easy way to set off the lead when 
setting the valve is : Take the distance between the lines/ 
and g plus the lead, in the dividers, then place one leg of the 
dividers at line g, and have the line e on the valve brought 
to the other point of the dividers, when the valve will have 
opened the port to the right amount. The engine must now 
be turned to the opposite dead-center, and the amount of lead 
noted. If the lead is the same on the back center then the 
steam-valves will have been set correctly. We will again 
turn our attention to the exhaust valves, this time for the 
purpose of adjusting them for compression. As the exact 
amount can only be determined satisfactorily by trial we will 
say that our engine is to have two and one-half inches com- 
pression, that is, the exhaust-valves must be set so as to close 
the exhaust-port when the piston is within two and one-half 
inches of the end of the stroke. To do this we measure off 
two and one-half inches from each end of the guides and 
make a line with the scriber. Now turn the engine in the 
direction it is to run, until the cross-head has nearly com- 
pleted its outward stroke and has reached the line on the 
guide. By means of the lines on the end of the valves and 



SETTING CORLISS ENGINE VALVES. 93 

the right and left adjustment in the rod, connecting that valve 
with the wrist-plate, have the valve moved (if it needs 
moving) until the line representing the edge of the valve 
comes exactly opposite the line representing the edge of the 
port. This marks the point of exhaust closure for that end. 
Then turn the engine around in the same direction until the 
cross-head reaches the line at the opposite end of the guides. 
The opposite exhaust-valve is then set in precisely the same 
manner as the first. 

Now we are ready to adjust the governor to produce an 
equal cut-off at each end of the cylinder. On the spindle of 
most Corliss engine governors will be found a stop device, 
in the form of a loose pin, or a removable collar. This device 
is for the purpose of preventing the governor from reaching 
its lowest position, for when it reaches the latter position the 
catch-block on the valve-stem arm should not be engaged by 
the hook. Should the governor belt break or slip badly, the 
governor would stop and reach its lowest position on the 
spindle, and as the valves cannot be opened when it is in this 
position the admission of steam to the cylinder is entirely shut 
off and the engine will come to a standstill. 

It will be apparent from the foregoing that the stop at the 
lower part of the governor spindle should be rendered 
inoperative, either by hand or automatically, as soon as the 
engine has attained full speed, and should again be placed in 
active position when about to stop the engine, as at noon or at 
night. 

As the stop device just mentioned determines the lowest 
position of the governor at which the valves should hook on, 
we will block up the governor and insert the stop. Un- 



94 SETTING CORLISS ENGINE VALVES. 

hook the reach-rod from the wrist-plate, and by means of the 
starting-bar move the wrist-plate over until the lines a and c, 
Fig. 86, are nearly opposite each other. The head-end valve 
should now have opened the port nearly wide, which may be 
ascertained by the marks on the end of the valve. Now 
adjust the governor-rod so that the projection on the disc 
operated by the governor will come in contact with the inner 
member of the hook, and so that the valve will be tripped or 
released when the marks a and c t Fig. 86, are exactly in line. 
As all governors do not move an equal amount to produce a 
given change in the point of cut-off, it will be safer to hook 
the reach-rod on the wrist-plate and have the engine turned 
in the direction it is to run, until the head-end valve is 
released. Then to adjust the cut-off at the crank-end, 
measure the distance the piston has moved in the forward- 
stroke, beginning at the cylinder end of the guides. Then lay 
off the same distance, beginning at the crank-end of the 
guides. Now have the engine turned round in the same 
direction as before, until the cross-head nearly reaches the 
last mark made on the guide, which will be nearer the 
cylinder-end of the guides. 

Unhook the reach-rod and turn the wrist-plate round until 
the marks a and d f Fig. 87, are nearly opposite each other, 
then adjust the length of the rod from the governor until the 
projection on the disc operated by the governor comes in 
contact with the inner member of the hook, and, so that the 
valve will be released when the cross-head reaches the last 
mark referred to and the marks a and d are exactly in line. 
Then will both valves cut off at the same point in the forward 
and return strokes respectively. In order that the same 



SETTING CORLISS ENGINE VALVES. 



95 



mean effective pressure, and consequently the same amount 
of work be performed in each end of the cylinder, the cut- 
off at the crank-end should be a trifle later than at the head- 
end. This is due to the fact that the piston area is reduced an 
amount equal to the area of the piston-rod. 

As the difference in the cut-off required is small and is 
dependent upon the area of the piston-rod, this adjustment of 
the cut-off can be more accurately made by the aid of the 




Fig. 89. 

indicator. At the upper part of the governor spindle, and a 
few inches above the counter-weight is another stop in the 
form of a collar, usually held in place by a set-screw, and is 
for the purpose of limiting the highest position of the governor. 
This collar should be placed at such a height, that when the 
governor is blocked up to it, the steam-valves cannot hook 
on. In case of breakage of the line shaft or main belt, the 
engine upon being relieved of its load will immediately run 



96 



SETTING CORLISS ENGINE VALVES. 



faster and until the counter-weight reaches the collar referred 
to, when the admission of steam to the cylinder being entirely 
shut off, the speed of the engine will at once slacken to the 
normal no-load speed. The valve-chest covers may now be 
put on, when the work of setting and adjusting the valves will 
be completed. 

In the foregoing it has been assumed that the type of 
valve-gear employed was the same as shown in Fig. 74. If, 




Fig. 90. 

however, it had been of the type shown in Fig. 89, we should 
have had to proceed a little differently when setting the 
eccentric. The difference referred to may be understood by 
referring to Figs. 90 and 91. 

Fig. 90 represents the principle of the gear which has just 
been described. It will be noticed (see Fig. 74) that as the 
eccentric, eccentric-rod, wrist-plate, etc., move toward the 
crank, the valve opens the port at the head-end of the cylin- 



SETTING CORLISS ENGINE VALVES. 



97 



der, therefore the piston, eccentric and wrist-plate move in 
the same direction. This explains why the eccentric in this 
case was moved in the same direction in which the engine 
was to run. 

Turning to Fig. 89, the principle of which is represented 
in Fig. 91, we find that when the piston moves forward or 
towards the crank (this direction being indicated by the large 
arrows) the wrist-plate and eccentric must move in the 
opposite direction to that of the piston, in order to open the * 




Fig. 91. 

port at the head-end of the cylinder. It is evident from this, 
that when setting the valves of a Corliss engine provided with 
a releasing gear of the type shown in Fig. 89 the eccentric 
must be turned in the opposite direction to that in which the 
engine is to run, until the valve opens the port to the amount 
of the lead. 

The work of setting the valves of a Corliss engine having 
two eccentrics is not particularly complicated as many 
engineers seem to think that it is, After inspecting the type 



oS 



SETTING CORLISS ENGINE VALVES. 



Table Showing Lap and Lead of Valves of Corliss Engines* 







Wrist-Plate in 


Crank 


BMrt 


Size of 


. 5 
S 2 


Central Position 


on 
Dead- 


ass. 




O fl 

S 1 




Center. 


Engine 






Ss£S 






o £ 


Steam 


Exhaust 


Steam 


•3 a 1 * oS 






Valves 


Valves 


Valves 


«-2<Sa 




H 


Lap. 


Lap. 


Lead. 


£ OQiS'd 


8 X 24" 
10X24 


100 
90 


J- 5-32" 


3-64" 


- 


if 


12X30 
12X36 


90 
80 


[• 3-16 


1-16 




J* 


14X36 
14X42 


80 
80 


- 1-4 


1-16 


- 1-64" 


2H 


14X48 


75 








2Y% 


16X32 


85 








1% 


16X36 
16X42 


80 
75 


► 5-16 


3-32 




2 

2X 


16X48 


70 






' 


2V4 


18X36 


75 








3 


18X42 


70 








18X48 
20X42 


65 
70 


- 3-8 






2% 
2* 


20X48 


65 








2% 


20 X 60 
22X42 


65 
70 


< 




■ 1-32 


3 

2M 


22X48 
22X60 


65 
65 


- 13-32 


- 1-8 




2% 


24X42 


80 








2H. 


24X54 


72 


; 






2% 


24X60 


60 








2% 


26X48 


65 




: 




W* 


26X60 
28X48 


60 


- 7-16 




* 


2H 


65 




5-32 




2X. 


28X60 


60 








3 


28X78 


55 






- 3-64 


3* 


30X48 


65 








3* 


30X60 


60 


'h 15-32 


y 3-16 




Stt 


30X72 


55 


i 




■ 


3* 



SETTING THE VALVES OF THE BROWN ENGINE. 99 

of releasing-gear employed and knowing in which direction 
the engine is to run, finding the direction in which to turn the 
eccentric becomes a very simple matter. When setting the 
steam-valves we have one eccentric to turn as in the case of 
the single eccentric engine* and when setting the exhaust 
valves another eccentric must be turned, but this does not 
add complication to the work, although it requires a little 
more time. The full side of the steam and exhaust eccentrics 
when set, stand approximately opposite each other, the exact 
position, of course, being determined by the required position 
of the valves. The work of centralizing the position of the 
various parts, equalizing the movements and setting and 
adjusting the gear is precisely the same as in the case of a 
single-eccentric engine. 

After setting the valves and making the final adjustments 
the engine should be started under steam and the work 
verified by the use of the indicator. 

This is especially true where the valves are set when the 
engine is cold. 

Setting the Valves of the Brown Engine. 

(Side Shaft Pattern.) 

The Brown engine, as will be seen by an inspection of the 
drawings, is a slide-valve engine in which valves of the grid- 
iron or multiported type are employed. The operation of 
the valves and method of setting them, however, differs con- 
siderably from that in what is commonly known as a slide- 



* For the practical limit of cut-off in the single-eccentric engine see 
The Engineer November 15, 1899. 

L.ofC. 



100 SETTING THE VALVES OF THE BROWN ENGINE. 

valve engine. As far as the distribution of steam in the 
cylinder, and consequently; the appearance of an indicator 
diagram taken from a Brown engine are concerned, they are 
identical to those obtained in a Corliss engine. Fig. 92 
represents a side view of the valve gear at the cylinder. It 




Fig. 92. 

will be noticed that the eccentrics in this engine are at the 
cylinder instead of being fixed on the main shaft. The side 
shaft is driven by means of a train of gears (three) from the 
main shaft and a pair of bevel gears located under the main 
bearing, the necessary bearing for these gears and side shaft 
being attached to the main bearing pedestal. In order that 



SETTING THE VALVES OF THE BROWN ENGINE. IOI 

the operation of the steam and exhaust-valves may be made 
more clear we will consider their functions separately, begin- 
ning with the steam-valves, a side sectional view of which is 
shown in Fig. 93. The steam-valves are carried by and at 
the upper end of the valve-stem s, the lower end of which is 
attached to the upper end of the stirrup a. In the stirrup is 
located the hook b, and attached to the lower end of the 
stirrup is the rod from the dash-pot. The lever or arm c is 
carried by the auxiliary shaft d y Fig. 93, and through which 
the governor changes the position of the arm. The operation 
of the steam-valves is as follows : 

The eccentric e t carried by the side shaft, revolves in the 
direction indicated by the arrow, and after passing the lower 
center begins to raise the littery, the inner end of which 
engages the hook in the stirrup, thus raising the valve also. 
The valve continues its upward movement until the lower 
end of the hook engages the arm c on the governor-shaft. At 
this point the hook is released from the lifter, and the dash- 
pot at once draws the valve downward^ closing the ports and 
effecting the cut-off. 

It will be seen from this that the point of cut-off is regulated 
by the governor in changing the position of the arm c and 
causing the hook to be tripped, thus releasing the valve 
earlier or later during its upward movement, according to the 
load on the engine. The exhaust-valves lie in a horizontal 
position and immediately below the bore of the cylinder, as 
shown in Fig. 94. These receive motion from the side shaft 
by means of a cam-wheel g> in the groove of which is a roller 
carried at the lower end of the rocker-shaft //. To the upper 
end of the rocker shaft is connected the exhaust-valve stem. 



102 SETTING THE VALVES OF THE BROWN ENGINE. 




Fig. 93. 



Setting the valves of the brown engine. 103 




Fig. 94. 



104 SETTING THE VALVES OF THE BROWN ENGINE. 

When a Brown engine is first erected the valves are proper^ 
set and all parts accurately marked ; therefore should the 
valve-gear become changed by the mere slipping of an 
eccentric or cam-wheel, the work of resetting the valve or 
valves becomes a very simple matter and one not requiring 
any particular skill, for in this case it is only necessary to 
bring the marks into their original position and tighten the 
set-screws. In case the trouble is due to wear, or to the 
presence of, numerous marks, which are too often found on 
this type of engine, rendering it impossible to determine the 
position of the valve in the chest by means of a given mark ; 
a different mode of procedure must be resorted to. 

If the engine is undergoing general repairs and time is not 
of such importance as when running, the removal of the 
cylinder-head and piston will greatly facilitate the work of 
setting the valves correctly, as both the steam and exhaust- 
valves may then be seen through the ports, and their exact 
position determined. However, the more probable method 
of resetting the valves of a Brown engine will be one that does 
not necessitate the removal of the cylinder-head and the 
piston, especially the latter, so we will consider such a method. 

We will assume now that the engine has been running 
and the several parts are correctly assembled as in Fig. 92. 
After placing the engine on the dead-center farthest from the 
cylinder, adjust the height of the stirrup at the crank-end 
of the cylinder by means of the threaded end of the rod 
from the dash-pot, so that the lifter will just engage the hook 
when the eccentric is on the lower center, or in its lowest 
position. Mark the height of the stirrup at the top of 
the guide z, Fig. 92. Remove the guide and the cap screw./, 



SETTING THE VALVES OF THE BROWN ENGINE. I05 

then raise the valve-stem clear of the stirrup and remove the 
chest, valve and stem from the engine, and lay on a table so 
that the valve may be seen. Remove the stem from the nut 
in the back of the valve, then, after taking the valve out of 
the chest, return the valve-stem to the nut and place the valve 
against its seat on the engine, connect the valve-stem to the 
stirrup when the valve will occupy its normal position minus 
the valve-chest. After raising and lowering the valve as the 
case may require and until the valve has the proper lap, mark 
the position of the stem relative to the top of the stirrup ; this 
may be done by making a mark on the stem close to the 
stirrup and another on the latter. Now turn the eccentric in 
the direction in which it runs until the lifter has raised the 
valve a sufficient distance to open the ports to the amount of 
the lead. Mark the height of the stirrup at the top of the 
guide as before. Then the distance between these two marks 
on the stirrup will indicate the lap of the valve plus the lead, 
see Fig. 92. Again place the valve on the table, being 
careful not to move the valve-stem in the nut in the back of 
the valve. 

Unscrew the stem from the nut counting the number of 
revolutio?is made until the stem leaves the nut. Place the 
valve in the chest and again insert the stem in the nut giving 
It the same number of turns as zvas required to take it out. 

The chest, valve and stem are now put in place on the 
engine, and the valve-stem inserted in the stirrup and secured 
by the cap-screw, bringing the lines on the stem and stirrup 
into proper position. After bringing the side shaft to its 
proper running position, which will be indicated by the clutch 
k t Fig. 92, the eccentric may be turned in the direction in 



I06 SETTING THE VALVES OP THE BROWN ENGINE. 

which it runs until the lower mark on the stirrup registers 
with the top of the guide. The eccentric being fixed in this 
position, the valve will have opened the port to the amount of 
the lead. The same operation is to be repeated at the head- 
end of the cylinder. 

In the case of the smaller and medium sizes of Brown 
engines, it may prove a saving in time to remove the cylinder- 
head, for this may be found easier than removing the valve- 
chest, and by so doing the steam and exhaust-valves at the 
head-end may be set by sight from the inside of the cylinder, 
through the port and without disconnecting the valve-gear. 
All that is necessary in this case is the removal of the guide 
i\ then loosen the cap-screw j\ Fig. 93, which will allow the 
valve-stem to be turned in the nut in the back of the valve. 

The mechanism employed in operating the exhaust-valves 
is extremely simple, and so constructed that derangement is 
practically impossible, except that due to the slipping of the 
upper arm of the rock-shaft, or the cam-wheel, and these can 
be quickly adjusted without disconnecting any of the 
members of the valve-gear. Suppose the usual marks on the 
side shaft have been removed. Take off the collar /, Fig. 92, 
and two marks will be found as shown in Fig. 94. The 
distance between these marks represents the lap of the 
exhaust-valve. 

With the aid of the gauge or tram as shown, the valve 
may be brought to its original location in the following 
manner : Turn the cam-wheel so that the lower arm of the 
rocker-shaft is in its extreme position nearest the cylinder, 
then place the tram in the position shown and move the 
upper arm until the mark nearest the cylinder registers with 



SETTING THE VALVES OF THE BROWN ENGINE. lO? 

the end of the tram. Secure the upper arm of the rocker- 
shaft at this point. 

To set the exhaust-valve, turn the engine in the direction 
it is to run until the cross-head arrives at the point where 
compression is to begin. If the engine is to have two and 
one-half inches compression, turn the engine over until the 
cross-head is within two and one-half inches of the end of the 
stroke, then turn the cam-wheel on the side shaft in th^ 
direction it is to run until the outer mark, see tram Fig. 9^ 
registers with the end of the tram. In this position the 
exhaust-valve will have just closed the port. 

The same operation is of course to be gone through with at 
the opposite end of the cylinder. If, for any reason, no marks 
appear at the upper end of the rocker-arm, as would be the 
case if an entirely new stem had been put in, then the 
exhaust connections at the under side of the exhaust-chest 
must be removed and the valve-seat blocked up in place, 
when the valve may be set by sight from the under side of 
the valve-seat. 

After setting an exhaust-valve in this manner, the tram 
should be applied and marks accurately made for future use. 

To Equalize the Cut-off. 

On the auxiliary or governor-shaft, and opposite each 
stirrup, will be found a vertical arm as at c t Fig. 93, the one 
at the crank-end being held by set-screws only, while the one 
at the head-end is held by a set-screw and a tapered pin. 

Having set the arm at the crank-end so as to admit of the 
latest cut-off, which should not exceed seven-sixteenths of the 
stioke, the equalization of the cut-off is effected by moving 
the arm at the head-end of the cylinder only. 



108 SETTING THE VALVES OF THE BROWN ENGINE. 

Pulling the tapered pin out allows of a later cut-off, and 
pushing it in causes an earlier cut-off. After the cut-off 
(latest) at the crank-end has been established, that at the 
head-end is to be made the same as the cut-off at the crank- 
end, and by means of the tapered pin a very nice adjustment 
of the cut-off may be had. 

Reversing the Engine* 

The side shaft in a Brown engine should always turn in the 
same direction, as indicated by the arrow, Fig. 93, regardless 




Fig. 95. 



of the direction in which the engine runs. It will be seen 
from this that the direction of the engine is not to be changed 
by altering the position of the eccentrics on the side shaft, 
but by removing the bevel-gear m y Fig. 95, and placing it in 
the position represented by the dotted lines. To accomplish 
this it will be necessary to loosen the set-screws in the several 
collars and other members of the valve-gear carried by the 
side-shaft, including the bevel-gear m. The crank, of course 
should be on either one of the dead-centers. Then slide the 



SETTING THE VALVES OF THE BROWN ENGINE. IOg 

side shaft toward the cylinder until the bevel-gear can be 
removed and placed as shown by the dotted lines. The side- 
shaft is then to be pushed back to its proper place and the 
various members brought to their positions by the marks 
provided for that purpose, except the bevel-gear which is to 
be set last, and can only be set when the shaft has been 
brought to its proper running position. 

Having all the parts properly set with reference to the 
side-shaft, and the clutch in its running position, have the 
side shaft turned in the direction in which it runs until the 
lower of the two marks on the stirrup at the end of the cylin- 
der, corresponding to the position of the crank, registers with 
the top of the guide z, Fig. 93, as previously described. It 
should be said that in turning the side shaft upon this occasion, 
the shaft should be turned from the crank end and so as to keep 
the clutch up tight and in the working position. With the above 
mark in proper position at the top of the guide— have the set 
screws tightened in the bevel-gear. The engine will then be 
ready to run in the opposite direction. 

The cylinder dimensions of the Brown engine closely 
approximate those of the Corliss engines, therefore the lap, 
lead, and trial compression given in a previous chapter for 
the Corliss engines will be found applicable to Brown engines. 
Setting the valves of this type of engine while hot will not be 
found to be as practicable as in some other types therefore it 
is very important that the indicator should be applied soon 
after the engine is started and the final adjustments of the 
valve-gear made by the aid of an indicator diagram. 



Examination Questions Answered. 



7. What qualities and qualifications should characterize 
a safe and reliable steam engineer? 

In order to become reliable, and a safe person to be in 
charge of steam machinery, one must be temperate. There 
is no place in the steam engineering field for a drunkard, and 
any person aspiring to the position of steam engineer, and 
who hopes to have charge of a modern steam-plant, cannot 
afford to use intoxicating liquors as a beverage. He should 
understand the principles involved in generating steam in a 
steam boiler, and those involved in a steam engine, pump, 
condenser and injector, in fact, all the accessories to steam 
machinery in general use, as well as having a practical 
knowledge, gained by experience, of the proper care and 
management of the various apparatus of which a modern 
steam-plant is composed. He should be in possession of the 
senses of sight, hearing and smelling, and be at all times 
observant of things about him. With these qualities com- 
bined with the desire to know the cause and effect of the 
various operations and processes connected with the running 
of steam engines and boilers and a determination to do every- 
thing well, he will possess the qualifications to be looked for 
as well as those necessary, to become a safe and reliable 
engineer. 

2. (a) What studies besides those of reading- and 



EXAMINATION QUESTIONS ANSWERED. Ill 

writing do you consider necessary for one to be proficient in 
order to become a successful engineer, and (b) -what are the 
duties of a n engineer? 

(a) Arithmetic, natural philosophy and spelling, in the 
order given. When the steam engine' first became a com- 
mercial success and the largest factories then in existence 
were being equipped with the new motive power, compara- 
tively little was known of the many ways of using steam 
economically, for the data available were limited, and more 
or less unreliable. Engineers in those days were expected to 
know how to start and stop the engine and locate any disorder 
that might arise in it ; that was about all. After these years 
of advancement and experience it is not unusual that 
engineers are expected and required to know much more 
concerning that kind of machinery and apparatus, the care 
and management of which form their business, and possibly 
their life work. Arithmetic comes first, for with it we can 
also obtain an additional knowledge of reading, writing, 
spelling, grammar and punctuation, and it includes the second 
and fifth branches named. Natural philosophy, or physics, 
forms the stepping-stone to the profession of steam engineer- 
ing, embracing all the principles made use of in the 
construction and operation of every piece of apparatus 
entrusted to the care of the engineer, (b) The duty of the 
engineer while in the engine-room is to give his whole time 
and attention to the care and management of every piece of 
apparatus in his charge, seeing that the steam pressure is 
carried uniformly and that the lawful or safe pressure is not 
exceeded ; that the water is carried at the proper level, and 
not permitted to get too high, nor too low ; that the fires are 



JI2 



EXAMINATION QUESTIONS ANSWERED- 




EXAMINATION QUESTIONS ANSWERED. 



"3 



properly attended to and the fuel used to the best advantage, 
and that the journals are regularly oiled and not allowed to 
get hot and to cut ; in short he must keep his eyes and ears 
open, and be ready to act promptly in case of emergency. 

j. What machine or apparatus in every steam-plant 
should receive the most careful attention and why? 

The steam boiler. The boiler is, practically speaking, the 




Water-Tube Boiler. 

source of the energy produced in every steam-plant. The 
pressure gauge shows the pressure of steam on one square 
inch of surface, so that the total force tending to pull asunder 
the plates of a boiler may be obtained by multiplying the 
number of square inches upon which the steam acts by the 
pressure indicated by the gauge. In rather small boilers this 
will be found to be several tons, which easily accounts for the 



114 



EXAMINATION QUESTIONS ANSWERED. 



disastrous effects of boiler explosions. It is due to the enor- 
mous force held within its narrow confines, that the boiler 
should be given the first and most careful attention by the 
engineer. 

4. Name the different tyfes of boilers in common use. 
The types of boilers in general use are : Water-tube, 
return tubular, return flue, locomotive, vertical tubular, drop 
flue, and Scotch (marine). 




Locomotive Boiler. 

J. What is the difference between a Jlue, tubular and 
water-tube boiler? 

A tubular boiler consists of an outer cylindrical shell, into 
the heads of which are expanded a number of tubes (see 
return tubular boiler answer to question 3) through which the 
smoke and gases pass on their way to the chimney. A flue 
boiler is much the same as the tubular except that the heat- 



EXAMINATION QUESTIONS ANSWERED. 



"5 



conducting passages through the boiler are larger, fewer in 
number and are generally riveted to the heads instead of 
being expanded into them. The tubes are four inches in 
diameter or less ; flues are more than four inches in diameter. 
A water-tube boiler consists of a number of tubes through 
which the water circulates, the steam rising into a drum at 



■ p 



Scotch (Marine) Boiler. 

the top. The fire and hot gases surround the tubes in the 
water-tube boiler. 

6. What is a boiler? a~$ump? an injector? 

A boiler is a machine for converting water into steam by 
the application of heat. An injector is a machine for rais- 
ing and moving liquids by means of a steam-jet. A pump is 
a machine for raising and moving liquids and compressing 
air and other gases. 

7. Name the different seams in a boiler. 



n6 



EXAMINATION QUESTIONS ANSWERED. 



The seam extending lengthwise of a boiler or dome, is 
called the longitudinal seam, those running round the boiler 
at the heads and ends of the plates are called curvilinear or 






Vertical Tubular Boiler. 



ring seams. The seam at the base of the dome is called the 
saddle-seam or dome-seam. The seam connecting the cylin- 
drical portion of a locomotive boiler to the fire-box is called 
the waist, and those in the water legs the leg-seams. The 



EXAMINATION QUESTIONS ANSWERED, 



117 



same applies to the water legs of a vertical boiler, which are 
also called bottom ring seam, and top ring seam, as the case 
may be. 

S. What is the difference between a single and double 




Drop Flue Boiler. 

riveted seam? What is meant by the safe-working pressure 
of a boiler? 

A single-riveted seam has but one row of rivets to hold the 
edges of the plates together, while a double-riveted seam has 



Il8 EXAMINATION QUESTIONS ANSWERED. 

two rows, and the triple-riveted seam has three rows. The 
longitudinal seams are usually double and triple-riveted, the 
curvilinear or ring seams usually being single-riveted. The 
curvilinear seams usually resist the pressure of steam against 
a portion of the boiler head only, while the longitudinal 
seams must resist a stress tending to pull the plates asunder. 
The latter joint not being aided by braces, tubes, etc., must 
resist a much greater stress than the ring seams. The safe- 
working pressure of a boiler is the highest pressure the boiler 
is capable of carrying with safety, and is usually taken at one- 
fifth the bursting pressure. The true safe-working pressure 
of a boiler cannot be ascertained without taking into account 
the strength at the seams, particularly the longitudinal seams, 
for the pressure on them is nearly double that on the ring 
seams. 

g. What is meant by tensile strength? 

If the tensile strength of boiler plate is 60,000 pounds per 
square inch of section, it will require a force equal to 60,000 
pounds, applied in the direction of its length, to pull asunder 
a bar one inch square, or a bar having an area of one square 
inch, whether it is one inch square or not. 

10. What are braces for, and zvhere are they f laced in 
boilers? 

To assist the surfaces to which they are attached in 
resisting the tendency of the steam to force them outward. 
In horizontal return tubular boilers the braces extend from 
a point on the shell to the head, for the purpose of holding 
the flat surface of the head in its proper position, or from 
bulging outward. Braces also extend from the top of the 
dome to the sides, and to the top of the shell for the purpose 



EXAMINATION QUESTIONS ANSWERED. 



no 



of relieving the seams of much of the strain due to the 
pressure of steam. In locomotive and vertical boilers what 
are known as stay-bolts are screwed into the inner and outer 
plates forming the fire-box, to relieve these plates of the strain 
due to the steam pressure. The crown-sheet in locomotive 
boilefs is stiffened by means of crown-bars, which are in turn 
held up by stays screwed and riveted into the outer shell.- 

//. Hozv is the safe-holding ^pouuer of braces calculated? 

Multiply 6,000 by the area of the brace at the smallest 





Lever Safety Valve. 

diameter, or at the bottom of the thread of a stay-bolt. The 
number of braces or stay-bolts is obtained by first multiplying 
the number of square inches of unsupported surface by the 
maximum pressure of steam in pounds, then dividing the 
product thus obtained by the safe-holding power of one bolt. 
The pitch or distance between the centers of stay-bolts is 
found by dividing the total area in square inches to be braced 
by the number of stay-bolts. The square root of the quotient 
will be the pitch in inches. 



120 



EXAMINATION QUESTIONS ANSWERED. 



12. Hovj many kinds of safety-valves are there? What 
are the advantages of each kind. 

Practically two. The lever safety-valve and the spring 
valve. The lever valve is the cheaper form of valve, and a 
little the easier to adjust to a given pressure, but requires a 




Spring Safety Valve. 



greater valve area and hence a larger valve, to discharge a 
given volume of steam in a given time. Owing to the pecu- 
liar construction of the spring or pop valve, the latter rises 
further from its seat when " blowing," and hence does not re- 



EXAMINATION QUESTIONS ANSWERED. 121 

quire so large an area. For portable engines, locomotives 
and marine service the "pop valve is particularly well adapt- 
ed, owing to the absence of the lever and ball. 

ij. How is the required area of a safety-valve obtained ? 

Divide the area of the grate in square f^et by three, for a 
spring-loaded, or pop safety-valve, and by two, for the lever 
and weight valve; the quotient will be the area of the valve 
in square inches. The following table gives the proper area 
of the valve for one square foot of grate surface: 

Press, by giuge ... 10 20 30 40 50 60 70 80 9J 100 110 r.0 
Area sq. inches.... 1.2.79 .58 .46 .33 .33 .29 .25 .23 .21 .19 .17 

14. (a) Hovu do you calculate the pressure at which a 
safety-valve zuill blow ? (b) How is the distance between the 
center of the ball and the fulcrum calculated ? (c) Hovu do 
you calculate the -weight of the ball required ? 

(a) Multiply the weight of the ball in pounds by the dis- 
tance between the ball and fulcrum. Call this product A. 
Multiply one-half the weight of the lever by the distance be- 
tween the valve and fulcrum = product B. Multiply the 
weight of the valve and stem by the distance between the 
valve and fulcrum = product C. Multiply the area of the 
valve in square inches by the distance between the valve and 
fulcrum = product D. Add together products A, B and C, 
and divide by product D ; the quotient will be the pressure, 
(b) Multiply the pressure by the area of the valve and by the 
distance between the valve and the fulcrum = product E ; 
multiply one-half the weight of the lever by the distance be- 
tween the valve and the fulcrum = product F ; multiply the 
weight of the valve and the stem by the distance between the 
valve and fulcrum = product G ; add together products F 



122 EXAMINATION QUESTIONS ANSWERED. 

and G, and subtract the same from product E ; divide the re- 
mainder by the distance between the center of the ball and 
fulcrum ; the quotient will be the weight of the ball, (c) Add 
together products F and G and subtract from product E as 
before. Divide the remainder by the weight of the ball ; the 
quotient will be the distance between the fulcrum and the 
center of the ball. 

75. What is meant by the terms, (a) heating surface, (b) 
grate- surface, (c) steam-room, (d) atmospheric pressure, (e) 
latent heat ? 

(a) All surfaces having water on one side and fire or heat- 
ed gases on the other, (b) The surface of the grate-bars, or 
the area of the surface which supports the burning fuel, (c) 
The space above the water-line, or all space in a boiler not 
occupied by water, (d) The pressure of the atmosphere 
which is taken at 14.7 pounds per square inch, and is equiva- 
lent to a column of mercury 30 inches high, at sea level (e) 
Latent means invisible, not apparent; therefore, latent heat 
means a quantity of heat which has disappeared, having been 
employed to produce some change other than elevation of 
temperature. By reversing that change the quantity of heat 
which has disappeared is reproduced, and may be' ascer- 
tained, or measured. 

16. How is the pressure of the atmosphere measured ? 
How may a vacuum be measured -without a vacuum gauge ? 

By means of a column of mercury, as in a barometer. If 
the mercury stands 30 inches high when open to the atmos- 
phere, the pressure may be found by multiplying 30 by .49, 
(the weight of a column of mercury one inch high) = 14.7 
pounds. When applied to a condenser should the mercury 



EXAMINATION QUESTIONS ANSWERED. 123 

rise but four inches high the pressure in the condenser would 
be 4 X 49 = 1.96 pounds. This would be equal to a vacuum 
expressed in pounds of 14.7 — 1.96= 12.74, and a vacuum 
gauge would indicate 12.74 -s- .49 = 26 inches. 

iy. Hovu do you find the number of square feet of heating 
surface in a (a) horizontal tubular, (b) locomotive, (c) ver- 
tical boiler ? 

(a) Multiply the inside circumference of one tube by the 
length, both in inches, and by the number of tubes. Divide 
the result by 144 and the quotient will be the number of 
square feet of surface contained in the tubes. Multiply two- 
thirds the circumference of the shell by the length, both in 
inches, and divide the result by 144; the quotient will be the 
number of square feet of surface in the shell. From the area 
of one head subtract the combined area" of the tubes and di- 
vide by 144; the quotient will be the effective surface in the 
heads. Add together the three results thus obtained; the sum 
will be the total number of square feet of heating surface, 
(b) Add the width of the fire-box to twice its height; multiply 
this sum by the length = product A. Multiply twice the 
width of the fire-box by its height, all in inches == product B. 
Add together products A and B. From this sum subtract the 
area of all the tubes and the fire-door. Divide the remainder 
by 144; the quotient will be the number of square feet of 
surface in the fire-box. The circumference of one tube mul- 
tiplied by the length, both in inches, and by the number of 
tubes will give the square inches of surface in the tubes; this 
divided by 144 will be the number of square feet. The sum 
of the number of square feet in the fire-box and tubes will be 
the total heating surface, (c) Multiply the height of the fire- 



124 EXAMINATION QUESTIONS ANSWERED. 

box by the circumference in inches = product C. From the 
area of the crown sheet subtract the combined area of the 
tubes and fire-door = product D. Multiply the inside cir- 
cumference of one tube by the length or height to the water 
line, both in inches, and by the number of tubes = product 
E. Add together products C, D and E and divide by 144; 
the quotient will be the number of square feet of surface. 

18. What is meant by the term horsepower when allied 
to a steam boiler ? 

There is, strictly speaking, no such thing as horse-power 
of a boiler. The term horse-power refers to the measure- 
ment of power, or energy produced in a given time. A boiler 
does not produce energy, therefore the work of a boiler can- 
not be measured by horse-power. Energy is the product of a 
given force in pounds multiplied by the distance in feet 
through which it moves, and horse-power is obtained by di- 
viding the energy thus obtained in one second by 550, in one 
minute by 33,000, and in one hour by 1,980,000. A boiler con- 
tains a force only, therefore the term horse-power is merely 
relative, and when applied to a boiler conveys to the mind 
the horse-power of an engine which a boiler of given size is 
capable of supplying with steam. 

ig. Which will safely carry the higher pressure, other 
things being equal> a boiler J2 inches in diameter or one 42 
inches in diameter ? Why ? 

A boiler 42 inches in diameter. The amount of surface 
contained in a boiler 72 inches in diameter is 72 h- 42 = 1.71 
times that in a boiler 42 inches in diameter, therefore, having 
the same steam pressure in both boilers, the force tending to 



EXAMINATION QUESTIONS ANSWERED. 125 

pull the plates asunder in the 72-inch boiler will be 1.71 times 
that in the 42-inch boiler. 

20, Hoiv far from the shell should the top of the bridge- 
wall and grates be? 

The principal object in the use of the bridge-wall is to 
form the back end of the furnace, and it should be high 
enough to retain the coal in the furnace when the deepest 
fires are being carried on the grates. There is no particular 
advantage in having the bridge-wall higher than is necessary 
to accomplish this, let the distance from the shell be what it 
may. The distance between the shell and grates should 
never be less than one-half the diameter of the boiler for bi- 
tuminous coal, nor less than four-tenths the diameter of the. 
boiler for anthracite. The distance from the shell to the top of 
the bridge-wall will then be from 14 to 20 inches according to 
the size of the boiler. 

21. Hozu do you determine the number of square feet of 
grate surface required for a boiler? 

The grate surface required will vary with the quality of 
fuel to be burned. Good bituminous coals require the least 
and slack coals the greatest number of square feet. With the 
former coal a ratio of 45 to 50 is allowed, and with the latter 
from 38 to 45. A boiler in which the ratio of grate to heating 
surface is 45, would have one square foot of grate surface to 
45 of heating, therefore if the heating surface is known the 
grate surface may be found by dividing the heating surface 
in square feet by the ratio as given above. When the weight 
of water to be evaporated per hour is known, the grate sur- 
face required may be found by dividing the weight of water 
in pounds by 94, or multiplying by .0106. 



126 EXAMINATION QUESTIONS ANSWERED. 

22, ( a) How do you find the safe-working pressure of a 
boiler? (b) How thick should the shell of a y 2-inch boiler be, 
to safely carry a pressure of go pounds per square inch? 

(a) The safe-working pressure may be found by either of 
the following rules: Rule i: Subtract the diameter of rivet 
hole from; the pitch of. the rivets, and divide the remainder by 
the pitch of rivets, all in inches, and call this quotient, i; then 
multiply the thickness of plate by the tensile strength in 
pounds and by quotient i. Divide the product thus obtained 
by five times the internal radius of the shell, the quotient will 
be the safe-working pressure. Or by Rule 2: Multiply the 
thickness of the plate in inches by 16,000 and divide by the 
diameter of the boiler in inches; the quotient is the safe- 
working pressure. The thickness of shell is found by multi- 
plying the pressure in pounds per square inch, by the diame- 
ter of the boiler in inches, and dividing the product by 16,- 
000; the quotient will be the thickness in inches, (b) By the 
rule given above the thickness would be 90 X 72 -J- 16,000 = 
.45 of an inch, the nearest obtainable thickness being seven- 
sixteenths. 

23. What points should receive particular attention when 
connecting up a water-column, a steam-gauge and a safety- 
valve? ( 

The column pipes should be of ample size, of extra heavy 
pipe and never less than one inch in diameter. The upper 
pipe should enter the dome or steam drum as the case may 
be; the lower pipe should enter the front head of the boiler 
at such a height that the bottom of the water glass, (or lower 
gauge cock) will be not less than one and one-half inches 
jbove the top row of tubes. The column pipes should be as 



EXAMINATION QUESTIONS ANSWERED. YI'J 

free from bends as possible. Tees should be used instead of 
elbows, to facilitate cleaning, and care taken to have the 
lower pipe level. The column should be provided with a 
blow-off pipe of ample size, closed by a gate-valve. Where 
the water contains much foul matter or mud, it is advisable 
to put gate-valves in the column pipes near the column, to 
secure full pressure when blowing out the lower pipe. The 
pressure gauge should be located in as cool a place as possi- 
ble, not too far from the boiler. The gauge pipe should be of 
such form that a little water may be introduced before screw- 
ing the gauge on, so that the gauge will be filled with cold 
water at all times. Provision should also be made for drain- 
ing the gauge pipe and gauge during freezing weather, when 
there is no steam in the boiler. The safety valve should be 
placed on the top of the dome, or steam drum, having as di- 
rect and short a connection as possible. No valve or branch 
pipe should be placed between the safety valve and boiler. 
If a lever valve, care should be taken to have the lever and 
valve-stem work freely, also that the ball is secured to the 
lever, and will not come in contact with any pipe, valve or 
other obstruction. 

24* How do you find the commercial rating, or horse- 
$ovuer of a boiler? 

By first finding the number of square feet of heating sur- 
face, (see answer no. 17) and dividing by 12, which gives what 
is known as boiler-makers' rating. If the evaporative capac- 
ity of the boiler is given, expressed in pounds of water from 
and at 212 degrees f. per hour, or at 70 pounds gauge pres- 
sure, from feed at 100 degrees f. the boiler h. p. may be found 



128 EXAMINATION QUESTIONS ANSWERED. 

by dividing the weight of water evaporated by 30 and 34, re- 
spectively. 

25. Hozu is the evaporative power of a boiler obtained? 
By multiplying the area of the graVe in square feet by the 

weight of coal burned per hour on one square foot and by 
8.2, the product will be the evaporation in pounds per hour. 

26. Hovu are boilers sullied zvith vuater — name the vari- 
ous methods. Which do you consider the most economical 
method ? 

By means of pumps, injectors, and gravity. A belt-driven 
pump forcing water through a good feed-water heater before 
it enters the boiler is probably the most economical means of 
feeding a boiler, all things considered. Next to this comes 
the duplex direct-acting steam pump, employing a feed-water 
heater as before. The injector is a very convenient as well as 
cheap form of boiler-feeding apparatus, but when used with- 
out a feed-water heater the economy is but little better than 
it is with a pump under similar conditions. 

27. What qualities should characterize all methods of 
feeding boilers ? 

Ample capacity, accessibility, reliability, simplicity and 
the ability to supply the boiler continuously with the maxi- 
mum amount of water required. 

28. At what temperature does water boil under atmos- 
pheric pressure ? Does the pressure of steam in a boiler 
have any effect upon the boiling point, if so -what effect? 

At 212 degrees f. When the pressure upon the water is 
increased, as in a steam boiler, the boiling point is raised, for 
it requires more heat to overcome the cohesion of its atoms 
than at atmospheric pressure. At 50 pounds by the gauge 



EXAMINATION QUESTIONS ANSWERED. 



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I30 EXAMINATION QUESTIONS ANSWERED. 

the boiling point is raised to 298 degrees; at 100 pounds, 338 
degrees; and at 150 pounds, 366 degrees. 

2g. What joints should characterize a good furnace 
grate ? 

Large air space — at least 55 per cent (see illustration, in 
which both grates have the same amount of air space) — deep, 
thin bars, so made as not to warp easily, provision for shak- 
ing, and also for dumping when the boilers are crowded, and 
a poor quality of fuel is in use. 

jo. About zuhat is the economical limit of coal consumption 
<per square foot of grate fer hour with natural draft ? 

About 24 pounds with a steady load, otherwise from 18 to 
20 pounds. 

31. (a) What is a chimney ? (b) What determines the 
intensity of the draft ? (c) Uj>on zuhat does the capacity of 
a chimney chiefly defend ? 

(a) A vertical flue, usually of iron or brick, for conveying 
the heated air and combustion gases from the fire to the outer 
air. It usually extends some distance above the tops of build- 
ings, (b) The height. The intensity of the draft increases 
directly as the height, ^c) The height and area. The capac- 
ity of a given chimney varies as the square root of its height. 

32. What is the difference between natural^ induced and 
forced draft ? 

Natural draft is that produced by a chimney alone, and is 
due to the difference between the weight of a column of the 
hot gases inside the chimney and an equal column of air on 
the outside. Induced draft is obtained by placing a fan 
blower at, or above, the boilers. The uptake from the boilers 
is connected to the inlet of the blower, and the outlet is car- 



EXAMINATION QUESTIONS ANSWERED. I3I 

ried to the chimney, discharging the gases and heated air into 
the chimney. Forced draft is obtained by conducting the dis- 
charge of a powerful blower to the ash-pit — the air being 
forced through the fire. 

33. What is your theory of the production and pre- 
vention of smoke ? 

Smoke is the volatilized products of the combustion of 
the fuel, and is invariably the result of incomplete combus- 
tion. It is composed chiefly of minute particles of carbon 
and steam, and is due largely to an excess of air admitted to 
the fire although in a few cases the production of smoke has 
been due to an insufficient supply of air to the fire. If the 
boiler is not crowded, and the draft is good, allowing the coal 
to coke at the front of the grates, afterwards pushing it back 
over the incandescent coals, will serve to reduce the volume 
of smoke. The hollow bridge-wall provided with suitable 
means for regulating the supply of air also gives good results 
where there is a strong draft. A small grate area and a very 
hot fire will reduce the volume of smoke, as will a very large 
grate area and a slow fire, although the former is the more 
economical. 

34. Explain your method of banking a fire. 

An economical manner of banking fires is to push the live 
coals back against the bridge-wall leaving the forward part of 
the grates covered with ashes only; then cover the live coals 
- with a moderately thick layer of fresh coal. Fine coal is pref- 
erable as the air does not readily pass through it, especially 
when the draft is diminished by closing the damper, which 
should be done just before covering the fire with fresh coal. 
The damper should be left open a very little to avoid the ac- 



132 EXAMINATION QUESTIONS ANSWERED. 

cumulation of gas in the furnace, and a possible explosion. 
This method of banking fires saves much time when prepar- 
ing to start again, as the grates may be quite thoroughly 
cleaned without disturbing the low fire at the bridge-wall, 
which is then pulled forward, spread evenly over the grates,, 
and fresh fuel added. 

jj. Should a boiler be fed intermittently or continuously ? 
Why ? 

When a boiler is used for heating purposes, and steams 
very easily, it does not make very much difference whether it 
is fed continuously or not, but a power boiler should be fed 
continuously, otherwise the water level becomes low. Aside 
from the ill-effects of expansion and contraction, and the dan- 
ger of having the water supply shut off when it is in this con- 
dition, when the feed-water is again started it must be intro- 
duced in larger quantities than if fed continuously. The 
feed-water entering the water in the boiler when the volume 
has been reduced, as at the time for " pumping-up," has a 
greater tendency to rapidly cool the water in the boiler. This 
invariably requires heavy firing to maintain the steam pres- 
sure The result is that more coal is burned than would have 
been necessary had the feed-water been introduced as fast a? 
it disappeared in the form of steam or by a continuous feed. 

j>6. What kinds of boiler-feeding apparatus are most 
favorable to continuous feeding ? 

A direct-acting duplex steam pump or one driven by .?<. 
belt, 

37. Should a boiler be fed vjith hot or cold zuater ? 
Why ? 

With hot waten Introducing cold water into a boiler tend* 



EXAMINATION QUESTIONS ANSWERED. 133 

io reduce the temperature of the water in the boiler, particu- 
larly in those parts near the opening of the teed-pipe, causing 
those parts to contract, which strains the plates and seams, 
more or less severely, according to the temperature and vol- 
ume of the water introduced. 

38, What effect do drafts of cold air have on boilers ? 
The same as introducing cold feed-water, though the 

strains produced are frequently more severe, often resulting 
in leaky tubes, seams and rivets, as well as a waste of fuel. 

39. Explain your method of cleaning boilers, and state 
about hovu often a boiler should be cleaned ? 

After shutting down the engine at night draw the fires, 
close the damper, with the fire and ash-pit doors partly open, 
allowing the boiler to cool down during the night. In the 
morning open the damper and ash-pit doors and empty the 
boiler, then remove the man-hole plate on top and the hand- 
hole plates from the head of the boiler, and by means of 
scrapers made for the purpose, proceed to scrape the mud 
and loose scale to the front end, where it may be removed 
through the hand-hole, Then enter the boiler through the 
man-hole, and scrape off all the scale and other accumula- 
tions as far as can be reached, seeing that the entrance to the 
column and blow-off pipe is clear, and lightly tap the braces 
to make sure they are tight. Then repeat the operation of 
scraping out below the tubes to remove large pieces of scale, 
after which the boiler is to be thoroughly rinsed with a hose. 
The plates are then returned to their places, the blow-off 
valve closed and the boiler filled with water. When the water 
makes its appearance in the gauge-glass open the column 
blow-off and rinse the blow-off pipe and bottom column con- 



134 EXAMINATION QUESTIONS ANSWERED. 

nections, then start a slow fire under the boiler so as to heat 
the water gradually until it begins to boil, when the fires may 
be hurried if need be. If the gauge-glass is properly located 
as to height, shut off the water when the glass becomes one- 
fourth full until after raising steam, then raise the water- 
level to the height required. The exact length of time a 
boiler may run without cleaning will depend upon the purity 
of the feed-water and the number of hours the boiler is in 
use during the day or week. The time for cleaning must be 
decided in each case. Boilers in cities located on such bodies 
of water as the great lakes are usually cleaned once a month, 
when running ten hours a day. If river water is used, such 
as the Ohio, Mississippi and Missouri rivers, a boiler running 
ten hours per day should be cleaned every two or three 
weeks. Boilers should be entered and scraped as thoroughly 
as possible, and carefully inspected as often as four times a 
year regardless of the location. 

40. At zvhat height should the zuater-line be maintained 
zvhen running ? 

This will depend upon the location of the water column 
and gauge-glass, as well as the amount of steam room in the 
boiler. The depth of water over the tubes should not be less 
than six inches in boilers supplying steam for engines. When 
the water-level is six inches above the top of the upper row 
of tubes, should the glass be half full, then this is the point 
at which the level should be maintained, which corresponds 
to two and one-half gauges. In this case, should anything 
occur to the pump or injector, it would allow from 15 to 20 
minutes in which to get the feed started again before the 
water-level would fall sufficiently low to cause a shut-down. 



EXAMINATION QUESTIONS ANSWERED. I3§ 

41. If the -water supply should be interrupted for an 
indefinite length of time, hozu and -what -would you do ? 

If the length of time the supply is to be stopped cannot 
be ascertained to within five or ten minutes, the engine 
should be shut down immediately. In any case the water- 
level should not be allowed to fall below one and one-half 
gauges before stopping the engine. If heavy fires are carried 
and the steam pressure increases rapidly, close the ash-pit 
doors and damper immediately upon the stoppage of the 
water supply. If the boiler contains plenty of water, allow 
the engine to run until the water-level reaches the second 
gauge; the steam pressure will then have been lowered so 
that stopping the engine will not cause the pressure to rise 
rapidly nor dangerously high. Should there not be enough 
water in the boiler to allow the pressure to be lowered in this 
manner, the fire may be covered with ashes, preferably wet, 
and the damper and ash-pit doors closed as before. 

42. Hozu ofte?i should the blow-off valve be opened? 
From two to four times a week where the feed-water is 

passably pure, but when using river water it should be 
opened at least once a day, preferably in the morning before 
a hot fire is had under the boiler. At this time much of the 
matter held in suspension in the water while the boiler is in 
operation, will have settled to the bottom and may be blown 
out, or may be allowed to run out. 

43. If you zvere obliged to stop the engine zvith a heavy 
fire in the furnace how -would you proceed ? Why ? 

Close the damper and the ash-pit doors and start the 
pump or injector to prevent the pressure from becoming dan- 
gerously high. If the water rises too high before the pres- 



I36 EXAMINATION QUESTIONS ANSWERED. 

sure ceases to rise, open the surface blow-off if there is one, 
if not, the boiler blow-off valve, and lower the water-level in 
this way, allowing the feed to continue until the fire dies 
down and the pressure ceases to rise. If it is impossible to 
keep the pressure down by feeding, when both the damper 
and ash-pit doors are closed, the fire may be covered with 
wet ashes, as in the case of interrupted water supply. The 
wet ashes, however, are to be used as a last resort. 

44, Illustrate your method of obtaining the percentage 
of saving by feeding a boiler with hot water, instead of 
cold. 

The percentage of saving may be found by the following 
rule: Divide the difference in the total heat of the water 
above 32 degrees before and after heating, by the total heat 
required to convert it into steam from the initial temperature. 
There are 1,180.7 heat units above 32 degrees in a pound of 
steam at 80 pounds gauge pressure, or 1,180.7 — (60 — 32) = 
1,152.69 above 60 degrees, which is the initial temperature of 
the water. The boiler would have to supply 1,152.69 heat units 
to make a pound of steam at 80 pounds pressure from water 
at 60 degrees. In raising the water to 140 degrees the heater 
supplies 140 — 60 = 80 heat units and the percentage of sav- 
ing is 80 -jh 1,152.69 = 6.94 per cent. 

43. To what would you first direct your attention upon 
entering a strange boiler room, or upon arriving in the 
morning ? 

The waiter-level in the boiler, and when taking charge of 
a strange boiler the source of the water supply and trie means 
provided for feeding the boiler should receive attention be- 
fore starting a fire. The true water-level may be ascertained 



EXAMINATION QUESTIONS ANSWERED. \yj 

by first opening a gauge cock above the water-level indicated 
in the glass, to allow air to enter the boiler. Then open the 
column blow-off and the drip to the gauge-glass; upon closing 
them again the level indicated by the glass should corres- 
pond with that found by opening the gauge cocks. 

46. Why do boiler tubes require cleaning, and about how 
often? 

The soot that collects in them is a non-conductor of heat, 
therefore when the surface of the tubes is covered with soot 
only a portion of the heat of the gases passing through them 
can get to the water surrounding the tubes. The remainder is 
carried to the chimney. A compact layer of soot in a boiler- 
tube, one-eighth of an inch thick, will cause as much waste 
of fuel as three-thirty-seconds of an inch of scale. When 
burning bituminous coal, soot will collect to the above depth 
in about ten hours, therefore, in order to have reasonably 
clean tubes at all times it is usually necessary to blow or 
scrape them at least once a day. 

47. How do you ascertain the true -water-level in a boiler 
when foaming? When griming? 

Foaming is usually caused by the presence of grease in 
some form. Therefore an endeavor should be made to 
change the water in the boiler as rapidly as possible. Slacken 
the speed of the engine, and start the pump or injector until 
the water-level will allow of from two to four inches being 
blown down, preferably by means of the surface blow-off, as 
much of the grease will be at the surface of the water. Con- 
tinue this operation until the water in the gauge-glass comes 
to rest when the true level may be ascertained as in answer 
45. Priming is caused by insufficient steam room in the 



I38 EXAMINATION QUESTIONS ANSWERED. 

boiler. The water-level in this case should be maintained as 
low as possible and yet be safe. A drum of moderate size or 
a large separator may be placed in the steam-pipe close to 
the engine. This will tend to increase the steam-room and 
at the same time will trap the water on its way to the engine 
should the boiler prime again. 

48. If the TV at er -lev el should become dangerously lozv, 
hozv zvould you proceed? 

Draw the fire immediately. Allow the engine to continue 
running, and prevent water from entering the boiler in any 
quantity. Do not open or close the valves nor tamper with 
the safety-valve. Allow the engine to run until it stops from 
lack of sufficient pressure, then close the throttle-valve. 
When the furnace has cooled down to about the same tem- 
perature as the boiler, the water-level may be raised very 
gradually until water appears in the glass, when it may be 
more rapidly filled, and the fire started. 

4Q. When steam in large quantities and at moderate 
pressures is required — often suddenly — zvhat type of boiler 
zvould you select? 

The horizontal return tubular boiler, on account of the 
large steam-space and water-surface at the water-line in this 
type of boiler, and because it is a comparatively cheap, eco- 
nomical and safe boiler. 

jo. If steam in large quantities and at high pressure is 
required zvhat type of boiler zvould you select ? 

The water-tube boiler, in whatever form, would best meet 
the conditions existing. Owing to the small volume of water 
contained in each tube, it is converted into steam very rapid- 
ly, and as the tubes are of small diameter they are capable 



EXAMINATION QUESTIONS ANSWERED. I39 

of carrying a very high safe-working pressure. These qual- 
ities render the water-tube boiler particularly well adapted to 
generating steam rapidly, and safely at high steam pressures. 

5/. Is boiler scale injuriotis to a boiler^ and does it affect 
the economical generation of steam? 

Yes ; in preventing the water from coming in contact with 
the plates and tubes, the latter are heated to a much higher 
temperature than would otherwise be possible, and too high 
for the good of the metal. Thick scale on the surface of a 
boiler causes unequal expansion of the plates and tubes, 
which results in leaky tubes, seams, rivets, and largely ac- 
counts for blisters and bagging, due to overheating at these 
parts. Scale retards the passage of heat from the fire and 
gases, to the water, thereby interfering with the rapid gener- 
ation of steam. The percentage of coal required to over- 
come the loss due to boiler scale is not definitely known. 

52. Explain various methods of removing and preventing 
scale. 

Kerosene oil removes old scale very effectually. About 
one-half pint of kerosene oil per day fed continuously into 
the feed-water will be found sufficient to remove scale as fast 
as it can be taken care of, by cleaning the boiler, and without 
danger of accumulating and causing serious over-heating. 
Scale may be to some extent, prevented by the use of a good 
compound, provided the water has been analyzed and the 
compound prepared particularly for the water being used. 
Mechanical boiler cleaners may be used with good effect, but 
with either method a boiler should be thoroughly cleaned at 
regular and frequent intervals if the full effect of the tend- 
ency to prevent scale-forming, is to be realized. 



140 



EXAMINATION QUESTIONS ANSWERED. 



53' What is a feed-water heater and for -what is it used? 
What is the difference between an open and a closed heater? 

A machine or apparatus for heating the feed-water by 
utilizing a portion of the heat in the exhaust steam, thus re- 
turning to the boiler a certain number of heat units that 
would otherwise go to waste. An open heater is one in which 
the exhaust steam comes in contact and mixes with the water 
to be heated. In a closed heater the exhaust steam is kept 
separate from the water to be heated, the water usually pass- 
ing through pipes surrounded by steam. 

54. To zuhat temperature may -water be heated in a closed 
heater , using- exhaust steam ? 

To about 210 degrees f. provided the heater is of the 
proper size. 

5J. Where should a feed-water heater be located and how 
should it be connected up with reference to the arrangement of 
pipe ? 

It should be placed as near the engine as practicable to 
insure as short an exhaust connection to the engine as possi- 
ble, and steam of the highest temperature possible in the 
heater. As steam parts with its heat more rapidly than water, 
it is better to allow the water to travel the greater distance. 
The feed-pipe should be as straight as possible, and provided 
with a gate-valve next to the boiler, then a check-valve, and 
a second gate-valve next to the heater, also a gate-valve in 
the inlet pipe close to the heater. 

j6. How would you determine the size of a heater re- 
quired for an engine of given h. p. ? 

Allow one-half square foot of pipe surface for one h. p. 
developed in the engine. 



EXAMINATION QUESTIONS ANSWERED. I4I 

J7. Which do you consider the better method, pumping hot 
water from the heater into the boiler, or forcifig cold zvater 
through the heater? 

A pump works much better and lasts longer, with fewer 
repairs, when pumping cold water, and may raise water from 
a well or cistern, which is impracticable when pumping hot 
water. In the latter case the pump must be located below 
the source of water supply. For these reasons it is prefer- 
able to pump cold water through the heater. 

jS. What causes the water to flow into the zvater cylinder 
of a pump? Does the temperature of the zvater have any in- 
fluence upon the height to zvhich a pump can raise it by suc- 
tion ? 

The pressure of the atmosphere. The plunger of the 
pump removes the pressure of the air from the surface of the 
water in the suction pipe, when the water is forced upward 
and into the pump cylinder by the pressure of the air on the 
surface of the water outside the pipe. As the temperature of 
the water increases, the height is decreased. Water at 60 de- 
grees f. can be raised by suction to a height of nearly 28 feet. 
A temperature of 140 degrees f. corresponds to a vacuum of 
23.5 inches of mercury, or an atmospheric pressure of 11.5 
pounds per square inch. A column of water 2.26 feet high 
weighs one pound at 140 degrees, therefore a pressure of 11.5 
pounds would support a column 25.99 ^ eet high* 

59. How is the capacity or duty of a pump expressed? 

In foot-pounds of work per million heat-units furnished by 
the boiler for large pumping engines, and in gallons per min- 
ute, or per hour, for medium and small sized pumps. 



142 EXAMINATION QUESTIONS ANSWERED. 

60. What information would you require in order to de- 
termine the $roj)er size of a steam $um£? 

The volume of water in cubic feet or gallons to be moved 
in a given time, the temperature of the water and the height 
to which it must be raised; also the length, and number of 
bends in the suction and delivery pipes. 

61. What is an injector ; and what advantages has it over 
a $um$? 

An injector is a machine for raising and forcing water by 
means of a jet of steam. It is smaller than a pump of like 
capacity, has no moving parts, requires the minimum of 
space, heats the feed-water and costs less than a pump of 
the same capacity. 

62. How do you find the number of gallons of -water 
that a fum^) of given size is capable of raising in a given 
time ? 

Multiply the square of the diameter of the water cylinder 
in inches by four, and by the piston-speed in feet per minute; 
divide the result by 120; the quotient will be the number of 
gallons per minute. 

63. Can a jiumj) force water against a pressure higher 
than that of the steam used to run the faimj)? How? 

Yes. A pump having six-inch steam cylinders and four- 
inch water cylinders, will be capable of forcing water against 
a pressure as much greater than that of the steam, as the area 
of a six-inch piston is greater than the area of a four-inch 
piston. The area of a six-inch piston is 28.27 square inches, 
and that of a four-inch piston 12.56 square inches, therefore 
the water pressure may be. 28.27 -f- 12.56= 2.25 times the 
steam pressure. 



EXAMINATION QUESTIONS ANSWERED. 143 

64. Why will an injector force -water into a boiler, when 
the pressures in the steam $i£e to the injector a?id boiler are 
equal'/ 

The mingled jet of steam and water rushes into the vac- 
uum formed by the condensation of the steam with such ve- 
locity that the momentum acquired carries it into the boiler. 

65. (a) What does a fressure-gauge indicate? (b) Should 
a gauge contain dry steam or -water? Why? 

(a) The pressure upon one square inch of surface, (b) 
Water. The bent tube which forms the spring in a pressure 
gauge moves very slightly when the pointer indicates ordi- 
nary pressures, and tends to lose its elasticity and become 
" set" when subjected to the temperature of steam 

66. If the pointer of a pressure-gauge fails to return to 
zero when there is no pressure in the boiler, what would 
you do? 

If the discrepancy exceeds three or four pounds, the 
gauge should be tested by one known to be correct and the 
pointer adjusted accordingly; if less than three pounds the 
pointer may be removed and set at zero before admitting 
pressure to the gauge. 

67. (a) What is an engine? (bj What do you under- 
stand by the term highspeed engine? (c) Slow-speed engine? 

(a) A machine for transforming the expansive force of 
steam into energy or work, (b) An engine running at a high 
speed of revolution — a fast running engine, (c) An engine 
running at a slow speed of revolution. A slow-speed engine 
may have as high a piston speed as the high-speed engine, 
therefore in this respect there would be no difference, al- 



144 EXAMINATION QUESTIONS ANSWERED. 

though in speed of revolution one engine might run twice as 
fast as the other. 

68. (a) Hozv do you denote the direction in zvhich a sta- 
tionary engine is running? (b) Hozv could you tell in zvhich 
direction an engine zvill run before the engine is started? 

(a) " Over" and " under." If the crank-pin, when leaving 
the dead-center nearest the cylinder, moves over the shaft in 
reaching the opposite dead-center the engine runs " over," if 
it moves dozvn and passes below the center of the shaft, then 
it runs " under." A locomotive engine when running forward 
or ahead, runs " under." (b) By an inspection of the eccen- 
tric, having first ascertained the kind of valve and valve-gear 
employed. 

6q. Hozv is the zvork performed by an engine, expressed? 

In foot-pounds and horse-power. 

70. What is meant by the term horse-fozver, and hozv do 
you find the horse- fiozver of an engine? 

One horse-power is equivalent to 550 foot-pounds per sec- 
ond (raised one foot high in one second) or 33,000 foot-pounds 
per minute or 1,980,000 foot-pounds per hour. The number 
of foot-pounds of energy generated by an engine may be 
found by multiplying the area of the piston in square inches 
by the m. e. p., and by the piston-speed in feet per minute. 
The product will be the number of foot-pounds per minute, 
which if divided by 33,000 will give the number of horse- 
power. 

7/. What do you understand by clearance in an engine? 

All the steam space between the valve and cylinder and 
between the cylinder head and piston when the latter is at 
the end of the stroke. Piston-clearance is the distance the 



EXAMINATION QUESTIONS ANSWERED. I45 

piston clears the cylinder head when the crank is on the dead 
center. 

72. State a method by which the percentage of clearance 
in a?i engine may be obtained. 

First secure a pail or other vessel having straight sides, 
that is, not tapered. Find the number of cubic inches con- 
tained in the pail for one inch in depth. Then place the crank 
on the dead center and move the valve enough to close the 
lead opening. Take out one of the indicator plugs and fill 
the clearance space full of water. Draw off the water through 
the cylinder cock into the pail, and multiply the volume of 
the pail for one inch in depth by the depth of water. The 
product will be the number of cubic inches contained in the 
clearance space. Multiply the area of the piston in square 
inches by the length of the stroke in inches, which will give 
the number of cubic inches in the cylinder, then divide the 
volume of water in the pail by the volume of the cylinder; 
the quotient will be the percentage of clearance. 

73. What is meant by piston displacement? Hozv do you 
find it? 

The volume of the cylinder, or the space passed through 
by the piston during one stroke. Multiply the area of the 
piston by the length of the stroke, both in inches; the product 
will be the piston displacement in cubic inches. 

7^. Hozv do you find the area of a piston? Also the pis- 
ton sfeed? 

Square the diameter and multiply by .7854. Multiply the 
length of the stroke in inches by two and divide the product 
by 12. This gives the piston travel for one revolution, then 
multiply by the number of r. p. m.; the product will be the 



I46 EXAMINATION QUESTIONS ANSWERED. 

piston speed in feet per minute. If the length of the stroke 
is in even feet, multiply the length of the stroke by two and 
by the number of r. p. m., and the. result will be the piston 
speed in feet per minute. 

75. Hoiv do you ascertain the m. e. £., terminal pressure, 
and number of expansions in an engine cylinder? 

To obtain the m. e. p. add one to the hyperbolic logarithm 
of the ratio of expansion, divide the sum by the ratio of ex- 
pansion and multiply the quotient by the initial pressure; 
from this subtract the back pressure. The remainder will be 
the m. e. p. The m. e. p. may be estimated by multiplying 
the initial pressure by the following decimals corresponding 
to the given cut-off, and subtracting the back pressure: 

Cut-off, % X H H % H % U 7 A 
Decimal, .48 .59 .67 .74 .84 .91 .93 .96 .99 

Divide the initial pressure by the number of expansions; the 
quotient will be the terminal pressure. Divide the length of 
the stroke, by the distance the piston has moved when cut- 
off occurs plus the clearance; the quotient will be the num- 
ber of expansions. 

76. What is the difference between a throttling engine 
and an automatic cut-off engine? A simple and a compound 
engine? 

In a throttling engine the cut-off is usually fixed, the 
speed of the engine being governed by means of a fly-ball 
governor in the steam pipe, which varies the pressure of 
steam admitted to the cylinder as the load changes. In an 
automatic cut-off engine, the pressure of steam remains the 
same, the speed being governed by varying the quantity of 



EXAMINATION QUESTIONS ANSWERED. 147 

steam admitted to the cylinder, and this is accomplished by 
the governor which changes the point of cut-off to suit the 
load. A simple engine is a single-cylinder engine exhausting 
into the atmosphere. If it is a condensing engine, then it is 
called a simple condensing engine. A compound engine is 
provided with two or more cylinders. The steam, after per- 
forming a certain amount of work in the first cylinder, passes 
into the second and performs additional work. From the sec- 
ond, or low-pressure cylinder, it passes to the condenser. If 
no condenser is used it is a compound non-condensing en- 
gine. 

77. Hovu do you find the h. j). of a compound condensing 



engine 



? 



Find the m. e. p. in both the high and low pressure C) lin- 
ders, either directly from an indicator diagram, or by the pre- 
ceding method. Add them together and divide the sum by 
the area of the low-pressure piston. The quotient will be the 
equivalent m. e. p. if all the work was done in the low-pres- 
sure cylinder. Then proceed to find the h. p. as directed in 
answer 69. 

j 8. What advantages has a compound over a simple en- 



gine 



? 



The principal advantage to be had in the use of the com- 
pound engine is a reduction in cylinder condensation. The 
range of temperature in each cylinder is considerably less 
than can be obtained in a single cylinder engine when em- 
ploying the same number of expan ,ons. When thus 
reducing the rate of cylinder condensation the steam may be 
expanded to a much lower pressure without loss, and conse- 
quently with a gain in power. Therefore a compound engine 



I48 EXAMINATION QUESTIONS ANSWERED. 

may develop more power with the same weight of fuel, or 
the same power with less fuel than the single-cylinder engine. 

79. Hoiv do you obtain the number of expansions in a 
compound engine ? 

Obtain the number of expansions in the high and low 
pressure cylinders separately (see answer 75) and multiply 
one by the other, the product will be the number of expan- 
sions. 

So. Explain your method of placing an engine on the ex- 
act dead-center. 

Turn the engine crank around until the cross-head is about 
one-half inch from the end of the stroke. With a scriber 
make a mark on the cross-head, extending it to the guide. 
Drive a wire nail through on*, end of a thin strip of wood of 
convenient length and place the strip in a vertical position, 
with one end on the floor close to the rim of the fly-wheel (or 
pulley) and with the point of the nail make a mark on the rim 
of the wheel. Now turn the crank over the center and back 
on the return stroke until the line on the crosshead again co- 
incides with the line on the guide. With the strip of wood in 
the same place and position make another mark on the rim 
of the wheel and with a flexible scale or pair of dividers, find 
the exact center between the two marks on the rim of the 
wheel and make a third mark at this point. Now, with the 
strip of wood in the same place and position as before, turn 
the engine crank around until the central or third mark made 
on the rim of the wheel reaches the point of the nail, when the 
engine will be on the exact dead-center. 
^ 81. Bozv zuould you proceed to line-uf an engine ? 

Remove the cylindier-head, piston and rod, stuffing-box 



EXAMINATION QUESTIONS ANSWERED. I49 

gland, crosshead and connecting-rod and turn the crank to 
the lower quarter,, First place a level on the shaft and level 
it, if need be, by raising or lowering the outboard bearing, 
as the case may require. Fasten one end of a stout cord or 
better still, a fine wire to some object beyond the crank and 
pass the other end of the wire through the stuffing-box and 
cylinder and fasten to some object as before. With a pair of 
inside calipers take the distance between the walls of the cyl- 
inder and wire at each end of the cylinder and also at one or 
more intermediate points, for the purpose of bringing the wire 
into the exact center of the cylinder. When the wire occupies 
a perfectly central position throughout the length of the cylin- 
der, turn the crank around until the crank-pin just touches the 
under side of the wire. When the pin occupies this position 
the distance from the wire to the inside of the shoulder or 
collar on the pin should be the same on both sides of the wire. 
It it is not, equalize the distance by moving the outboard 
bearing slightly, as the case may require. Now- turn the 
crank around and bring the pin up to the wire at the opposite 
center. Again measure the distance from the wire to the 
inside of the collar or shoulder as before, which should be the 
same as at the opposite end. If the engine is fitted with loco- 
motive guide-bars, or a single bar-guide, the distance from 
the wire to the guide should be taken with the calipers at 
each end of the stroke, equalizing the distance of the bar from 
the wire by slightly moving the guides as the case may require. 
Should the shaft be much out of line, requiring considerable 
movement of the outboard bearing, it would be advisable to re- 
move the quarter-boxes and scrape them to an even bearing, 
otherwise the shaft in its new position will be liable to bear 



I50 EXAMINATION QUESTIONS ANSWERED. 

very heavily at the ends of the quarter-boxes only and cause 
excessive heating. Replace all the parts removed and make 
the necessary adjustment with the crank on the dead-center. 
Turn the engine to the opposite dead-center and make sure 
that the crank passes the dead-center easily. 

82. What is meant by the terms (a) force, (b) energy, 
(c) fovuer? 

(a) A force is that which tends to produce motion, as the 
pressure of steam in a steam boiler, (b) Energy is repre- 
sented by the product of a force multiplied by the distance 
through which it moves regardless of the time required to 
move that distance, (c) Power is energy produced in a 
given time as per second, minute or hour, and like energy, is 
expressed in foot-pounds,, (For horse-power see answer 69). 

83. What does an indicator indicate ? Houu ? 

The pressure of steam in an engine cylinder, and at all 
points in the stroke of the piston. By a pencil carried at the 
extremity of the pencil lever which, when pressed against the 
card on the paper drum, traces a diagram. The vertical dis- 
tance measured from a line called the atmospheric line to 
any point in the line forming the diagram when multiplied by 
the number of the spring used, represents the pressure of 
steam in the cylinder at that point in the stroke of the piston; 
the pressure thus indicated being above the pressure of the 
atmosphere. 

84. Hovu is the m. e. f. obtained from an indicator dia- 
gram ? 

Divide the diagram into a number of equal parts length- 
wise, ten for ordinary work, and with a scale corresponding 
to the spring with which the diagram was taken, measure the 



EXAMINATION QUESTIONS ANSWERED. 15\ 

pressure along the center of the space between each of these 
divisions; that is, between the full lines or ordinates. This 
pressure must be measured between the lines of the diagram, 
whether the engine is condensing or non-condensing, and not 
from the atmospheric or any other line. Add together the 
pressures obtained at each ordinate, and divide the sum 
by ten, if the diagram is divided into ten spaces; the quotient 
will be the m. e. p. When the area of the diagram in square 
inches is known, the m. e. p. is obtained by dividing the area 
by the length of the diagram, then multiply the quotient by 
the number of the spring used when the diagram was taken. 

Sf. Describe an engine-room method of calculating the 
zi/ater consumption from indicator diagrams, 

13,750 divided by the m. e. p. will give the number of cubic 
feet of steam per h. p. per hour used by the engine if steam 
were admitted during the full stroke of the piston. The 
above quotient must be multiplied by that part of the stroke 
completed (after cut-off occurs) where the water rate is to be 
computed, expressed in decimal parts of the stroke, plus the 
percentage of clearance, in order to get the volume of steam 
used when cutting off at less than full stroke. The volume of 
steam thus obtained multiplied by the density or weight of 
one cubic foot of steam corresponding to the pressure at the 
point in the stroke where the water consumption is to be com- 
puted, will give the water consumption for the forward 
stroke. On the return stroke some steam is saved by com- 
pression. This is found by dividing the 13,750 by the m. e. p. 
as before, and multiplying by the percentage of the return 
stroke uncompleted at the point where the saving is to be 
computed, plus the percentage of clearance. The product 



152 



EXAMINATION QUESTIONS ANSWERED. 



will be the volume of steam saved, which multiplied by the 
density of the steam corresponding to the pressure at the 
point selected, will give the weight of the steam' saved. Sub- 
tract the latter from the former result, the remainder will be 
the number of pounds of water (steam) used per h. p. per 
hour. 

86. Can the exact weight of steam used by an engine be 
calculated by means of an indicator diagram ? If not, vuhy 
not? 

No. An indicator diagram shows the pressure in an 
engine cylinder, not the volume of steam admitted. When 

Percentage of Loss by Cylinder Condensation. 



Percentage of 


Simple 
Engines. 


Compound 


Trip!e Expan- 


Stroke Com- 


Engines, H. P. 


sion Engines, 


pleted at Cut-off. 


Cylinder. 


H. P. Cylinder. 


5 


42 






10 


34 


26 




15 


29 


24 


22 


20 


26 


22 


20 


30 


22 


18 


16 


40 


18 


15 


13 


50 


14 


12 


10 



exhaust takes place the walls of a cylinder are at a somewhat 
lower temperature, owing to the low pressure of the exhaust 
steam. The incoming steam heats up the cylinder walls 
which results in a portion of the steam being condensed, but 
as this loss is instantly made up by live steam, the pressure 
remains the same, therefore the indicator cannot show the 
volume of steam condensed, nor any variation in pressure. 
Cylinder condensation increases as the cut-off becomes 



EXAMINATION QUESTIONS ANSWERED. 



153 



shorter, or occurs earlier in the stroke, for the steam in the 
cylinder is then expanded to a lower pressure and conse- 
quently has a lower temperature. The percentage of steam 
lost by cylinder condensation is given in the table on the 
preceding page. 



Atmospheric Line 
Vacuum Line 






»v 




G > 


f \ 

R g 2 i 




^, 


7 




^z 






Atmospheric Li 
Vacuum Line 


ne. ^v. 



8j» Describe a method of drawing the hyperbolic curve 
on an indicator diagram ? 

First draw horizontal line CD, Fig. 1, parallel to the at- 
mospheric line. Draw perpendicular, A E placing the point 
A as near the point of cut-off as possible. Divide the line C 
D into any number of equal parts, 1, 2, 3, 4, etc., and fron; 



154 EXAMINATION QUESTIONS ANSWERED. 

these points draw diagonals to F at the intersection of the 
clearance and vacuum lines. From line CD let fall G E and 
from G E draw lines parallel to the atmospheric line meeting 
line A B at the intersection of the diagonals running to F. 
From the points I, 2, 3, 4, etc., drop perpendiculars to the 
several horizontal lines. The point of intersection of the 
perpendiculars with the horizontal lines from G E to A B 
marks the path of the hyperbolic curve, which is shown by 
dotted lines. 

88. Describe a method of obtaining the clearance in an 
engine by means of a diagram. 

Select a point on the expansion curve as at A, Fig. 2, and 
also at B before release commences. Draw lines C D and E 
^parallel to the atmospheric line. Draw perpendiculars E C 
and F D and diaw the diagonal G H. At the point where the 
line G H intersects the vacuum line raise the perpendicular / 
/. The distance between the lead line of the diagram and 
the perpendicular I/ 9 represents the clearance ; the width of 
this space divided by the length of the diagram will give the 
percentage of clearance. 

8q. What is a condenser, and zvhy are condensers at- 
tached to steam engines ? 

An appliance in connection with a steam engine for 
condensing the exhaust steam, thus producing a partial 
vacuum in the cylinder. The removal of the resistance (at- 
mospheric pressure) to the movement of the piston, tends to 
increase the m. e. p. and consequently the speed of the 
engine. If the load remains the same the cut-off will be 
shortened and a certain amount of steam will be saved at each 
stroke. On the other hand, when the m. e. p. is increased by 



EXAMINATION QUESTIONS ANSWERED. 155 

removing the atmospheric resistance to the piston, it will re- 
quire a heavier load on the engine to maintain a uniform 
speed, therefore more power will be developed. The removal 
of the pressure of the atmosphere by the condensers may be 
made to serve three purposes, first, a saving in fuel when, the 
load remains constant ; second, increased power when the 
load is increased, so as to maintain a uniform speed with the 
higher m. e. p., and third, in providing pure water for the 
boiler when a surface condenser is employed and the feed is 
taken from the hot-well. 

go. Hozv many types of condensers are there? Name 
them ? 

There are five types of condensers in use. The surface 
condenser in which the steam and condensing water are kept 
separate. The jet condenser in which the injection water 
mingles with the steam to be condensed. The injector-con- 
denser which employs the principal of the exhaust injector 
The siphon condenser in which the condensing water is 
raised to a height of about 30 feet, and descending through 
a "tail" pipe produces a vacuum. The two latter types 
require no air-pump. The air-cooled condenser in which a 
current of cold air is used instead of water, and resembles the 
surface condenser. 

gi. In case the vacuum gauge should fail, hozv could 
the vacuum be measured? 

By means of a column of mercury, as in a barometer. 
When the tube containing the mercury is open to the atmos- 
phere the latter will reach a height of about 30 inches, and as 
a column of mercury one inch square and one inch high 
weighs .49 of a pound, the pressure supporting 30 inches is 



I56 EXAMINATION QUESTIONS ANSWERED. 

.49 X 30 = 14.7 pounds per square inch. Now, if the tube is 
•connected to the condenser, and the mercury stands 3.5 inches 
high, the pressure supporting it is 3.5 X .49 = 1.7 pounds per 
square inch, therefore the pressure removed from the con- 
denser will be equal to the difference between the pressure 
of the atmosphere and that in the condenser, or 14.7 — 1.7 = 
13 pounds per square inch. The vacuum gauge indicating 
the absence of pressure in the condenser, which is usually- 
expressed in inches of mercury would show 13 -5- .49 = 28 
inches vacuum. (See answers to questions 16 and 58). 

Q2. How do you find the number of h, f. that may be 
transmitted by a single belt 20 inches wide ? 

By the following rule : Multiply the width of the belt in 
inches by the velocity in feet per minute and by 48 ; divide 
the product by 33,000, the quotient will be the h. p. A belt 
20 inches wide, running 2,500 feet per minute, will transmit ; 
20 X 2,500 X 48 -*- 33,000 = 72.7 h. p. For double belts 
multiply the above result by 1.3, thus 72.7 X 1,3 = 94.5 h. p. 
for a double belt. The rule for finding the width of a belt is : 
550 multiplied by the number of h. p. to be transmitted and 
divided by the speed in feet per minute, will give the width 
in inches, thus 94.5 X 550 -s- 2,500 = 20 inches. For single 
belts multiply the above result by 1.2. To find the length of 
a belt when closely rolled, add the diameter of the roll and 
the eye (in inches) together, multiply the sum by the number 
of turns or coils in the roll, and by 1309 ; the product will be 
the length in feet. To find the weight of a belt, multiply the 
length in feet by the width in inches, and divide the product 
by 13 for single and eight tor double belts. 



EXAMINATION QUESTIONS ANSWERED. 157 

03. Hozu are the speed and diameter of driving and 
driven pulleys calculated ? Give a rule. 

Rule for finding the speed of a driven pulley : Multiply 
the diameter of the driver in inches by the number of r. p. m., 
and divide by the diameter of the driven. To find the speed 
of the driver : Multiply the diameter of the driven by the 
number of r. p. m., and divide by the diameter of the driver. 
To find the diameter of the driver : Multiply the diameter 
of the driven by the number of r. p. m., and divide by the r. 
p. m. of the driver. To find the diameter of the driven : 
Multiply the diameter of the driver by the r. p. m. and divide 
by the r. p. m. of the driven. 

q4. Hovj many square feet of surface are there in a tube 
three inches in diameter and ten feet long ? 

The number of square feet in a tube of any size may be 
found by multiplying the diameter in inches by 3.1416 and by 
the length in inches, which will give the number of square 
inches of surface ; this divided by 144, the number of square 
inches in one square foot, will give the number of square feet. 
A pipe three inches in diameter and ten feet long will contain 
3 X 3.1416 X (10 X 12) -h 144 = 7.85 square feet. 

qj. How many feet of three-inch p>ife would be required 
to obtain 150 square feet of surface ? 

The number of square feet of surface required, divided by 
the square feet contained in the pipe for one foot in length, 
will give the number of feet of pipe. A pipe three inches in 
diameter has 3 X 3.1416 X 12 -s- 144 = .785 of a square foot 
for one foot in length, therefore to obtain 150 square feet will 
require 150 -r- .785 = 191 feet of pipe. 



I58 EXAMINATION QUESTIONS ANSWERED. 

g6. Hoiv is the required volume of condensing zvater 
calculated ? 

Multiply the weight of the steam to be condensed by the 
heat units given up by one pound of steam in condensing, 
and divide the product by the rise in temperature of the 
cooling water. Taking steam at 20 pounds pressure by the 
gauge, initial and final temperature of cooling water at 60 
and 108 degrees respectively and the weight of steam con- 
densed at 1,000 pounds, the quantity of cooling water will be 
1,193 X 1,000 --5- (108 — 60) = 24,854 p@unds, or 24,854 -s- 1,000 
== 24.854 times the weight or volume of the steam condensed. 

97. What is a receiver in an engine ? What is a sepa- 
rator? 

A receiver is a vessel or chamber used in connection with 
compound engines, into which the exhaust steam from the 
high-pressure cylinder is admitted and from which the low- 
pressure cylinder takes its supply. A separator is an appli- 
ance used to remove the entrained water from the steam pipe 
of an engine. 

g8. Hovj do you calculate the gain in $>ozver that may 
be had by adding a condenser ? 

Divide the pressure in pounds corresponding to the inches 
of mercury shown by the vacuum gauge, by the m. e. p. plus 
four when running non-condensing. If the vacuum gauge 
shows 26 inches of mercury and the m. e. p. is 34 pounds per 
square inch, the increase in power is 26 X 49 ■*- 28 = 38.5 per 
cent. 

no. Hozv do you calculate the saving in steam due to a 
condenser ? 

To the m. e. p. non-condensing add three pounds. In the 



EXAMINATION QUESTIONS ANSWERED I $g 

table of mean and terminal pressures find the cut-off that will 
produce this mean pressure (absolute), then subtract the cut- 
off so found, expressed in decimal parts of the stroke from 
that when running non-condensing, and divide the remainder 
by the latter cut-off, the quotient will be the percentage of 
steam saved. M. e. p. non-condensing is 34 pounds per 
square inch at three-eighths cut-off, and 34 -f- 3 = 37 pounds 
at five-sixteenths cut-off when condensing. The saving in 
steam is .375 — .3125 -f- .375 == 16.9 per cent. 

100. Hozu do you find the weight of water that may be 
ev a f orated by a given weight of coal ? 

Coal containing little or no incombustible matter will' yield 
about 14,500 heat units per pound. If there is 12 per cent of 
incombustible matter, there will be 88 per cent of 14,500 heat 
units available for steam making, or 14,500 X .88 = 12,776 
heat units. It requires 966 heat units to convert one pound of 
water into steam, from and at 212 degrees f. Therefore if 
there were no loss at the boiler, 12,776 heat units would evap- 
orate 12,776 -r 966 = 13.22 pounds. If the boiler evaporated 
10 pounds of water per pound of coal it would have an effi- 
ciency of 10 H- 13.22 === 75.6 per cent, a figure closely approxi- 
mated but seldom reached in practice. 

101. What is the meaning of the following terms : Laf, 
lead, admission, cut-off", expansion, exhaust or release, com- 
pression, and pressure of compression? 

See pages 4 to 11. 

102. How would you proceed to set a plain D slide-valve? 
See page 21. 

ioj. What do you u?idcrstand by the terms : Initial 



160 EXAMINATION QUESTIONS ANSWERED. 

pressure, average pressure, terminal pressure, backpressure 
and mean effective pressure? 

By initial pressure is understood the pressure of the steam 
in an engine cylinder at the commencement of the stroke and 
is equal to the boiler pressure, minus the losses due to friction 
and condensation in the steam pipe between the boiler and 
engine and also the loss in pressure due to wire-drawing at 
the throttle valve if such exists. The average pressure rep- 
resents a mean or average between the initial pressure and 
that at the point of release, and is obtained by adding 
together the pressures obtained at different points in the 
stroke and dividing the sum by the number of points at which 
the pressure was obtained. See page 150. By terminal pres- 
sure is meant the pressure of steam in the cylinder at the end 
of the stroke or at the point where the exnaust valve opens. 
See page 146. By back pressure is meant the pressure of 
steam in the cylinder which opposes the movement of the 
piston and is usually due to a portion of the steam used during 
the previous stroke remaining in the cylinder. In non-con- 
densing engines the back pressure is measured from the 
atmospheric line, or above the pressure of the atmosphere, 
and in condensing engines from a perfect vacuum. The 
mean effective pressure in any engine is equal to the average 
pressure minus the back pressure. 

104. What do you understand by the term vacuum? 

A vacuum is said to exist when the pressu-e of the at- 
mosphere has been removed ; a vessel from which the air has 
been expelled and the pressure therein reduced to a point 
below that of the atmosphere. 






JUN 101903 




